Midlength Gas Systems (split from the Colt Midlength thread)

[rob_s]

While I personally think that most of the midlength hype is just that, the fact remains that it's what the market thinks it wants, however stupid, uneducated, safe-stuffing, dirt-shooting, wannabe-operator that market may be. Colt, if they want to get serious about the hobbyist market, needs a midlength with a decent extended handguard from the factory. That's not physics, engineering, or TDP, that's marketing.

I, for one, can't wait to see this new offering. I've long been unable to tell someone "go down to Bass Pro and get an X" answer to the "what AR should I get?" question, since everyone wants (or thinks they want) a midlength and a gorilla-arm handguard. Frankly, the gas-tube length for me is maybe 10% of my enthusiasm for this new gun with the handguard being 90%. I sincerely hope they ship it with an MLOK QD swivel for the buyer to place as-desired, and a decent set of metal flip-up sites.

[split from the Colt Midlength (https://pistol-forum.com/showthread.php?19451-Colt-Midlength) thread --TJ]

[El Cid]

Yeah, a midlength gas system and some furniture is awesome progress. Their incision into the vast market void is breathtaking.

Colt is a pretty large company and takes longer to turn the corner. And it's more than a mid gas and Monty's new handguard. It's a free-floated factory Colt which only recently was available as the OEM2 and as a limited purchase for federal agents of a certain organization. In 2016 with optics as reliable as they are, and quality BUIS I don't see any reason to tolerate the FSB that Colt held onto for so long. I don't want my sling or hand guards touching my bbl and affecting POI. I don't want limited choices in where to put my light or hands unless I have the benefit of a SBR configuration. I don't want an iron sight taking up part of the view through my optic.

Nobody suggested it was a drastic change, and they are certainly late to the party. But many of us don't want or need the same carbine configuration my Dad used in 1965. Bottom line is if you don't like/want/need it, don't buy it. I'll never understand why people feel the need to go into a thread about something they don't want just to make a negative comment that is in no way constructive.

[HCM]

Frankly, the gas-tube length for me is maybe 10% of my enthusiasm for this new gun with the handguard being 90%. I sincerely hope they ship it with an MLOK QD swivel for the buyer to place as-desired, and a decent set of metal flip-up sites.

This ^^^^^

[M2CattleCo]

I think it's kind of funny that Colt is coming out with a mid-length about the same time most every mid-length on the market is over-gassed compared to a 6920.

I'm of the opinion that mid-length gas is pure b.s., but I own one, and my other three ARs are KAC SR-15s.

I'll buy one of these Colts for the barrel and the rail. Colt's chrome lined barrels are only equaled by KAC.

[breakingtime91]

I think it's kind of funny that Colt is coming out with a mid-length about the same time most every mid-length on the market is over-gassed compared to a 6920.

I'm of the opinion that mid-length gas is pure b.s., but I own one, and my other three ARs are KAC SR-15s.

I'll buy one of these Colts for the barrel and the rail. Colt's chrome lined barrels are only equaled by KAC.


I don't think it makes much of a difference but to call it bull shit is a stretch.

[orionz06]

I'm of the opinion that mid-length gas is pure b.s., but I own one, and my other three ARs are KAC SR-15s.


Why?

[StraitR]

I think it's kind of funny that Colt is coming out with a mid-length about the same time most every mid-length on the market is over-gassed compared to a 6920.

I'm of the opinion that mid-length gas is pure b.s., but I own one, and my other three ARs are KAC SR-15s.

I'll buy one of these Colts for the barrel and the rail. Colt's chrome lined barrels are only equaled by KAC.

IMO/E, the manufacturer determines (by choice or incompetence) whether or not a system will be over-gassed, not the system length itself.

It's interesting that you feel that way about mid-length's and at the same time only own mid-length's or longer (unless you have a ten year old SR15 M4).

[M2CattleCo]

I bought the KACs for the E3 bolt, barrel profile, and URX3.1. I bought the BCM mid for the SS410 barrel and KMR. I don't like the government profile and won't own one as they don't do anything for me.

If there was a carbine tube under all those 13"+ hand guards, it wouldn't bother me a bit.

[StraitR]

I bought the KACs for the E3 bolt, barrel profile, and URX3.1. I bought the BCM mid for the SS410 barrel and KMR. I don't like the government profile and won't own one as they don't do anything for me.

If there was a carbine tube under all those 13"+ hand guards, it wouldn't bother me a bit.

Indifference is fine, but your previous comment was much stronger. Why do you think mid-length gas is BS?

Can you give examples of "most every mid-length on the market is over-gassed compared to a 6920"?

[rob_s]

I happen to also think it's largely BS. The gas tube, gas pressure, gas fiddle-fuck thing is one of those cases where people start spouting a bunch of numbers and tests and shoulder feel but never really seem to come up with any sort of actual, measurable, tangible, benefits to the deviation.

I don't begrudge anyone the midlength, but I happen to think that where the bullets meet the target it's largely BS as well.

But, again, I think Colt's move here is more about marketing than engineering, and I'm fine with that.

[jeep45238]

Personally I think there's a lot to be said about keeping the dwell time of gasses to the bolt carrier group the same as the original design to keep the timing of events the same.

A rifle length gas tube on a 20" barrel, middy 16", and carbine 14.5" all have the gas port the same distance from the barrel to keep the dwell time the same, though they run different gas pressures due to the location of the gas port to the chamber.

I think it's interesting that the 20" with the least gas pressure runs the lightest spring with the heaviest buffer weight, and is of the original design; yet some manufacturers will run a longer dwell time with a higher gas pressure with a lighter buffer with an enlarged gas port.

[rob_s]

Personally I think there's a lot to be said about keeping the dwell time of gasses to the bolt carrier group the same as the original design to keep the timing of events the same.

A rifle length gas tube on a 20" barrel, middy 16", and carbine 14.5" all have the gas port the same distance from the barrel to keep the dwell time the same, though they run different gas pressures due to the location of the gas port to the chamber.

I think it's interesting that the 20" with the least gas pressure runs the lightest spring with the heaviest buffer weight, and is of the original design; yet some manufacturers will run a longer dwell time with a higher gas pressure with a lighter buffer with an enlarged gas port.

This is exactly the kind of red herring information I'm talking about.

Keep the dwell time the same why? What is going to happen if you don't? What's so great if you do? Does the gun become more accurate, more reliable, or last longer if the dwell time is the same? Different?

"Dwell time" is one of those seemingly meaningful terms that gets thrown around a bunch that doesn't actually mean anything tangible.

[nalesq]

I also don't find the argument that the mid-length is somehow better because it's "closer to the original design" to be particularly persuasive, as though the M4 variant is somehow new or novel. I mean, if over a decade and a half of global war isn't enough to vet a weapon as good enough to make its replacement not worthwhile anytime in the foreseeable future, I don't know what is.

Even the Jarheads are finally dumping their 20-inch muskets for the M4, which perhaps says something about the value of the "original design."

[jeep45238]

I also don't find the argument that the mid-length is somehow better because it's "closer to the original design" to be particularly persuasive, as though the M4 variant is somehow new or novel. I mean, if over a decade and a half of global war isn't enough to vet a weapon as good enough to make its replacement not worthwhile anytime in the foreseeable future, I don't know what is.

Even the Jarheads are finally dumping their 20-inch muskets for the M4, which perhaps says something about the value of the "original design."

M4's run a 14.5" barrel, not a 16" - and I never said original is better, just that keeping the gas lengths on those barrel lengths gives the same amount of time the bolt carrier is being acted upon. I think the middy on a 16" is the civilian equivalent of a 14.5" M4.



This is exactly the kind of red herring information I'm talking about.

Keep the dwell time the same why? What is going to happen if you don't? What's so great if you do? Does the gun become more accurate, more reliable, or last longer if the dwell time is the same? Different?

"Dwell time" is one of those seemingly meaningful terms that gets thrown around a bunch that doesn't actually mean anything tangible.

To start with, I'm not a subject matter expert. I'm not a high round count guy anymore, and I was never a door kicker. I have a bit of background in jet engine R&D, vehicle design and fabrication, and too many dollars down the tube chasing more torque and power out of cars without wanting to yank the engine in a apartment complex. I'm looking at things from a design standpoint, and I honestly think that Stoner's design is genius in it's implimentation. Will they dramatically fail if you don't? Not at all. If you're running quality gear you'll never worry about it. Will things last longer if you keep timing of operations similar or the same given a higher pressure? I think so.

But for a thinking exercise look at the $450 AR at every gun show with a huge gas port, carbine gas on a 16" barrel with the cheapest (lightest) buffer in the tube you can buy. This is scary because I don't think I'm that smart, but have been told I am - which to me says the folks specing these things out don't have a clue what they're doing besides copying the other guy for a buck cheaper. Thinking leads me to completely miss some things, but also dig really deep into other things to understand them. Sometimes the cycle comes round circle and I learn quite a bit, other times I just get pissed off and walk away in frustration. Thinking can be hard, and I don't like putting that effort into things I don't care about. But I like explosions and things that operate due to flamable things.

The downside of a longer dwell is the bolt trying to unlock under a higher pressure, and more stress on the lugs. I think we can all agree that the moment the bullet exits the barrel pressures begin to drop dramatically, and for every inch between the gas port and muzzle pressure is being exerted on the bolt, while pressure is going up. I don't want my internals subject to more stresses than what's required to make things operate as designed for longer intervals between parts replacement.



In a round about way the thing that has it making sense to me is to akin it to ignition timing in a gas engine. You'll make more power as you advance the timing more, but only to a certain point. Once you advance ignition to the point where peak pressure is happening prior to top dead center you're just putting more stress on bearings and internal components while not gaining any more oomph to the wheels. It's pretty wise to back off a degree or two at that point if you're on a street car for longevity purposes. The compression in the cylinder is similar in both situations, but the timing (optimzation of the controlled burn in the cylinder) is the key to keeping a connecting rod coming out of the oil pan.

[StraitR]

This is exactly the kind of red herring information I'm talking about.

Keep the dwell time the same why? What is going to happen if you don't? What's so great if you do? Does the gun become more accurate, more reliable, or last longer if the dwell time is the same? Different?

"Dwell time" is one of those seemingly meaningful terms that gets thrown around a bunch that doesn't actually mean anything tangible.

You're missing the point. This portion of the discussion started with mid-lengths are BS, not carbine gas sucks. They may very well be BS, but the people asking for clarification on why they are should not be the ones with burden of proof as to why they're not.

Has anyone found a actual, measurable, tangible reason why mid-lengths are inferior to carbine? Some prefer the carbine system because it's most proven. Fair enough, I subscribe to that and I'd take carbine too if thrust into a combat zone. But that alone doesn't make other gas lengths BS. The perfect gas system for all barrel lengths could be 8" for all anyone knows.

Let's not do anything crazy like try to make the AR better since we'll never get forty years of service and five wars under it's belt to validate the improvements. Where did the M4 come from again?

For whatever reason, people seem to think they need "combat proven" to shoot a few thousand rounds a year at paper targets. That seems pretty SHTFantasy to me, as you like to put it. I find it interesting that once the new hotness becomes commonplace, some people must find a reason to move on or move back. I can't wait for web gear and woodland camo to be back in style, I'll be all set.

I asked M2CC to clarify because he did a drive by with two fact based statements without any supporting information, but I got ambiguity. Other people asked the same "why" question, but got nothing. "That sucks" and a mic drop doesn't fly around here Rob, and you know that as well as anyone.

[JSGlock34]

Let's not do anything crazy like try to make the AR better since we'll never get forty years of service and five wars under it's belt to validate the improvements. Where did the M4 come from again?

I always thought this post by Trey Knight on M4C held a lot of insight into the limitations of always coloring between MILSPEC lines and gets at your point.


Any gun is as good as the weakest part of that gun. Cost has to be factored in . If a gun costs 3 times as much as another but lasts only twice as long is it better. The biggest problem with the entire M4 world is that gun is a compromise. The gun and round (M855) were originally designed around a 18" bbl platform. The gas system,buffer tube bolt, everything. When we compromised the design by hacking off the bbl and buffer tube things got funny. We(industry) have been trying to fix this compromise of stoner's design since it occurred. We have tried boosters,buffers,rubber bumpers, rocket wire extractor springs ,pistons , dual extractor springs , you name it. Most of the developments that became the M4 actually came out of a tanker gun program. The M4 was about as right as we could get it at the time. For procurement logistics and other reasons the design was frozen at this point. Can we (industry) make a better gun than a M4 perhaps but probably not for the same dollar and 100% parts commonality. As I stated a gun is as good as it's weakest link and the weakest link in 16" and under short gas system guns is the extractor . I would say it is a 3000 round life cycle. If I can change this $5 part on schedule then there should not be a problem. If I can't then that 5$ part could cause my entire rifle to be useless and as a soldier or someone else who depends on their rifle this way this 5$ part could cost them their life. The next point of failure would perhaps be the bolt. I'm not going to quote life cycle here because it is a not totally agreed on subject but with suppressor use it is certainly more limited. Last is the bbl. A hammer forged chrome lined bbl is going to last longer than other types of bbls. It may or may not be as accurate but when improperly maintained a HF CL bbl will beat out all others period. I am going to call the life cycle of a good HF CL bbl to be 20,000 rounds. There are certainly reports of them lasting shorter under heavier firing schedules , and it won't explode at this point but the accuracy will start to deteriorate at this point.

KAC has tried to build a rifle that all the parts will last the full 20,000 rounds. Zero parts replacement. The downside is it costs more and lack of parts compatibility .

The bottom line as I have said before the Mil spec requirement is certainly there for a reason. It is possible to build a gun that will perform better than a mil-spec gun that may not meet the requirement. Many people claiming Mil-spec may not actually meet that requirement for something as obscure as ISO certification.

There are so many good choices out there in the AR world . So many good companies doing innovative stuff . I would hate to see industry not advance the AR design because we are held to trying to just build mil-spec guns.

At what point does a gun not become an AR anymore? We all know that the non-full curve magazine is a weak link. Would you guys be willing to throw all your mags away in order to achieve a higher level of reliability? We(US gov't) were not willing to take that step with the SCAR.

Just some thoughts ;sorry for a rambling post , it is not meant to be a rant.

[StraitR]

I always thought this post by Trey Knight on M4C held a lot of insight into the limitations of always coloring between MILSPEC lines and gets at your point.

Yup, and he sounds a lot like his Father HERE (http://www.smallarmsreview.com/display.article.cfm?idarticles=1222) and especially HERE (http://smallarmsreview.com/display.article.cfm?idarticles=1211) in part 2 where Reed specifically speaks about the AR platform.

[Appalachained]

Colt's chrome lined barrels are only equaled by KAC.

I disagree. My Noveske 16" chrome lined shoots tighter groups than my 6920 with any kind of ammo. Not by much, but it definitely does.


Sent from my iPhone using Tapatalk

[JSGlock34]

Yup, and he sounds a lot like his Father HERE (http://www.smallarmsreview.com/display.article.cfm?idarticles=1222) and especially HERE (http://smallarmsreview.com/display.article.cfm?idarticles=1211) in part 2 where Reed specifically speaks about the AR platform.

Great reads; thanks for posting those interviews. I remember reading them years ago and I forgot all about them.


I disagree. My Noveske 16" chrome lined shoots tighter groups than my 6920 with any kind of ammo. Not by much, but it definitely does.

And amusingly Noveske's hammer forged chrome lined barrels were made by FN, whereas the barrel in my early SR15E3 was made by Colt Canada...

[Appalachained]

^^^^ So I hear. I need to put more magnification on my PSA premium just to see if it'll outshoot my 6920 too.


Sent from my iPhone using Tapatalk

[rob_s]

Better is better. Different isn't better.

[breakingtime91]

Better is better. Different isn't better.

Who said it was better? FWIW I would carry a mid length in afghanistan if I went back... I wouldn't cry if I had to carry a carbine gas system

[orionz06]

Yes! It's back to 2009 again.

[rob_s]

Who said it was better? FWIW I would carry a mid length in afghanistan if I went back... I wouldn't cry if I had to carry a carbine gas system

The only reason for deviation is improvement.

Well, that and separating suckers from their cash.

[breakingtime91]

The only reason for deviation is improvement.

Well, that and separating suckers from their cash.

lol ok man. this conversation isn't going to go anywhere.

[rob_s]

lol ok man. this conversation isn't going to go anywhere.

No, it's not.

Because the same old tired arguments for the midlength being better, with the same old buzzwords like "dwell time" will keep getting thrown about, by people with no knowledge base beyond what they were told online.

If midlength is not quantifiably better than carbine length in some capacity outside of Internet theory, then what's the point?

The KAC interviews are great and all, but what is the quantified improvement in their system over the legacy?

I'm not anti progress. I fiddle fucked and burned more money and time chasing new hotness for over a decade before I finally learned that nothing markedly better has come along.

To go back to the original point of the thread, at least the longer handguard has ergonomic and heat shield. Not to mention retained accuracy when braced, over the legacy, and the tapered barrel profile has the potential to be marginally more accurate.

[breakingtime91]

Yes! It's back to 2009 again.

exactly what I thought..

[JSGlock34]

I'm of the opinion that the single greatest small arms improvements over the past 20 years are in the field of optics. We're still launching the same bullets, but the guidance systems are much improved. As far as the KAC rifles go, as much as I like my SR15E3, I think the enhancements are arguably in the lifecycle/logistics realm and of little impact to the individual user. I certainly do not notice the improved barrel and bolt life when launching rounds downrange or measuring groups.

[orionz06]

The only reason for deviation is improvement.

Well, that and separating suckers from their cash.

Isn't carbine gas length on a 16" deviation too?


Sent from my Nokia 3310 using an owl

[jeep45238]

The only reason for deviation is improvement.

Well, that and separating suckers from their cash.



You do realize that your argument can be the same for those running anything besides a 20 inch barrel with a fixed stock right?

If you're going to use statements like red herring, you should actually understand what the fallacies of logical arguments are and start using things besides your opinions stated as if they are facts.

[ffhounddog]

I have found some suppressor combos with a midlength gas to not work as well as they do with a carbine gas. One of my Midlengths run fine with a suppressor and brass case ammo but not too well with Hornady Steel match or Silver Bear. My carbine Gas have no issues shooting steel case commie stuff with a suppressor. To me since getting in the Suppressor game full tilt, It is the way to go for me.

[M2CattleCo]

As far as me saying the mid length is BS... I should clarify that I mean the hype surrounding it is largely BS. The carbine length is in service with near every civilized nation in every climate the world has to offer. MANY out there with 16" barrels.

I've shot many Colt 6920s and 6921s, as well as mid lemgths from all the usual 'top tier' mfgs. My shoulder and shot timers tell me that a properly gassed Colt shoots softer, or at least faster, tham these mids. My highest round count AR (I trade/sell/swap/rebuild too much) went almost 20K of nothing but NATO 5.56 with zero parts breakage. it was a Colt
carbine.

I really do think the mid is a better mousetrap, but with the top mfgs porting 'em to be steel case reliable gassers, I lost interest. The whole point of it way back ten years ago was to optimize the 16" for 5.56. That's been lost IMO. Same as slick tube hand guards.

[Unobtanium]

No, it's not.

Because the same old tired arguments for the midlength being better, with the same old buzzwords like "dwell time" will keep getting thrown about, by people with no knowledge base beyond what they were told online.

If midlength is not quantifiably better than carbine length in some capacity outside of Internet theory, then what's the point?

The KAC interviews are great and all, but what is the quantified improvement in their system over the legacy?

I'm not anti progress. I fiddle fucked and burned more money and time chasing new hotness for over a decade before I finally learned that nothing markedly better has come along.

To go back to the original point of the thread, at least the longer handguard has ergonomic and heat shield. Not to mention retained accuracy when braced, over the legacy, and the tapered barrel profile has the potential to be marginally more accurate.

Check out the MARS-L dominating the last military trials it was entered in, in nearly every category.

[Chuck Whitlock]

No, it's not.

Because the same old tired arguments for the midlength being better, with the same old buzzwords like "dwell time" will keep getting thrown about, by people with no knowledge base beyond what they were told online.

If midlength is not quantifiably better than carbine length in some capacity outside of Internet theory, then what's the point?

The midlength is better than the carbine because you can mount a bayonet.....duh! :cool:

[rob_s]

The midlength is better than the carbine because you can mount a bayonet.....duh! :cool:

which is a far better reason than "because:dwell-time"!

[MistWolf]

There is some mythology being bandied about in this thread that should be addressed.

First- “Midlength is pure BS. It’s all hype and no engineering”.

From a technical viewpoint, the midlength does offer advantages over the carbine length gas system without any downside I’m aware of.

What you have to understand is that the gas port regulates flow not pressure. That means the gas port has to be the right size to flow the correct amount of gas to operate the action at the given pressure. If the port is too small, carrier acceleration will be weak and the action will short stroke. If the port is too large, carrier acceleration is excessive causing rapid wear of parts and sharp recoil.

How much gas flow through the port depends on port diameter and gas pressure. The larger the port diameter, or the higher the pressure, the greater the flow will be. The higher the pressure, the smaller the margin between the minimum port diameter and maximum port diameter needed for optimal flow. This means port diameter at higher pressures is more critical. It also means that port erosion has a greater impact on gas flow. As the midlength taps into the bore where pressures are lower than where the carbine gas port would be, port diameter is less critical and port erosion will have less impact on gas flow.

Another advantage is that the gasses from a midlength gas tube will be cooler as they enter the expansion chamber, compared to a carbine length. The longer the gas tube, the greater the cooling. We can see this during a heavy firing schedule. The gas tube will start glowing at the gas block, but is cooler further away. This is because the gasses have lost heat.

From a practical viewpoint, the advantages of the middy may or may not be worth changing from a carbine length rifle. A carbine gas system works and it works well, offering a good compromise the original designers intended, giving the military the shortest possible rifle that is reliable, durable and with a 14.5 inch barrel, can still mount a bayonet. It can be tuned to shoot softly, especially now as the industry and tuners understand the system better. Claims that the middy is a vastly superior system is over stating things. But it's a myth that the 16 inch middy offers no engineering advantage over a 16 inch carbine gas system.

Second- “Dwell time”. Let’s start by defining what “dwell time” is. It’s the time the bullet is in the barrel between the gas port and the muzzle. The theory is, the longer the dwell time, the longer the gas has to act on the action. it also states that, all else being equal, if dwell time is increased, the system will be over gassed and carrier speeds increased.

Pure bunkum.

Let’s take a closer look and see why. In order for the dwell time to have any effect on the operation of the AR, the gasses will have to start the carrier moving before the bullet exits the muzzle. That means the carrier will start moving when the bullet is a certain distance from the gas port and that distance will be the same no matter what the distance is from the gas port to the muzzle. That means that the barrel length from port to muzzle wouldn’t change anything. That means adding a suppressor would not cause over gassing. The pressure in the gas system would actually remain the same. Why? Because the bullet will be the same distance from the gas port every time the system is charged.

In fact, the gas doesn’t charge the system until after the bullet has left the barrel. The gas system operates off residual pressure. It takes time for the gasses to vent after the bullet uncorks the muzzle. As the pressure vents, pressure drops at the muzzle first and the pressure drops works its way back to the gas port, then the chamber. The longer the distance from gas port to muzzle, the more time the gas is pressurizing the gas system. This is also why a suppressor can cause severe over gassing. It’s designed to slow down the gasses, increasing venting time. The final nail in the coffin is physics. When a supersonic gas passes through a smaller orifice, it's slowed to the speed of sound. The gas traveling through the gas tube is much slower than the supersonic gas pushing the bullet down the bore. The bullet always reaches the muzzle before the gas in the tube reaches the carrier.

In case you're wondering, it takes about .25 milliseconds for the bullet to travel the distance between the carbine gas port and exit the muzzle of a 16 inch barrel.

The dwell time theory is not just a myth, but it's also bad science.

For the record, for every inch the bullet travels down the barrel, the pressure drops as the gas is having to fill an increasing volume

I've asked a friend who talked to Colt about the new middie. The word is "soon". We know what "soon" means

[orionz06]

But... But... But... We can't see differences in mid lengths so they must be bullshit. It makes us feel better to believe it.


/S


Sent from my Nokia 3310 using an owl

[rob_s]

The myth is that "engineering advantage" equals real world advantage.

[BWT]

My work here is done. :cool:

https://pistol-forum.com/showthread.php?21105-Things-that-will-absolutely-get-you-killed-on-the-streets&p=470463#post470463



...
149. not making an effort to keep the rain from ruining the rhubarb.
150. Getting hit by a bus.
151. The Midlength Gas System in an AR-15.
152. Advantageous Engineering Mythology.


God Bless,

Brandon

[orionz06]

The myth is that "engineering advantage" equals real world advantage.

What's the disadvantage?

[MistWolf]

The myth is that "engineering advantage" equals real world advantage.

The claim I was refuting is that there is no quantifiable advantage, not whether or not the advantage was worth it. But in this case, the engineering advantage does equal a real world advantage in long term reliability and durability. As the gas port of the middy taps into the barrel where the gasses are at a lower pressure and temperature, gas cutting will be reduced. Now, the question becomes "is the advantage worth it to you?" Whether the answer is "yes" or "no", it's subjective. It's a preference. For the most part, proper tuning is more important than gas port location.

For myself, it's a matter of efficiency. If the barrel has a carbine length gas system, the rifle is a more effective package if the barrel length is 14.5 inches or less. If the barrel length is going to be 16 inches, I want the advantages of the middy gas system. It's like when I look at an M4 barrel. I don't see an M203 notch, I see a carbine gas barrel with the cut line already laid out

[rob_s]

The claim I was refuting is that there is no quantifiable advantage, not whether or not the advantage was worth it. But in this case, the engineering advantage does equal a real world advantage in long term reliability and durability. As the gas port of the middy taps into the barrel where the gasses are at a lower pressure and temperature, gas cutting will be reduced. Now, the question becomes "is the advantage worth it to you?" Whether the answer is "yes" or "no", it's subjective. It's a preference. For the most part, proper tuning is more important than gas port location.

For myself, it's a matter of efficiency. If the barrel has a carbine length gas system, the rifle is a more effective package if the barrel length is 14.5 inches or less. If the barrel length is going to be 16 inches, I want the advantages of the middy gas system. It's like when I look at an M4 barrel. I don't see an M203 notch, I see a carbine gas barrel with the cut line already laid out

You must be an engineer.

The "advantages" you mention are theoretical until tested, and irrelevant until shown to have an impact on performance. "Gas cutting" is right up there with "dwell time", as far as I'm concerned.

But in any case, I'm still interested in this gun, as I think it makes a viable "first AR" suggestion (pending details, price point, etc.), in part because it has the mid-length gas system so that subscribers to that particular voodoo can check off their internet boxes.

But I'd be just as interested if it was simply a 6720 being sold with a Ceturion MLOK handguard.

Some of the pictures I see of this gun scare me though as they seem to have a bunch of "ambi" uselessness on them, which I suppose also addresses market demand and Internet checkboxes.

[Unobtanium]

Anything that allows one to better control the weapon, and has no downsides, is a plus. Considering how the MARS-L trounced everything in testing, I'd say that it's a plenty reliable concept.

[Unobtanium]

You must be an engineer.

The "advantages" you mention are theoretical until tested, and irrelevant until shown to have an impact on performance. "Gas cutting" is right up there with "dwell time", as far as I'm concerned.
Dwell-time is legitimate, as is "gas cutting". It's been shown again and again in the real world.
But in any case, I'm still interested in this gun, as I think it makes a viable "first AR" suggestion (pending details, price point, etc.), in part because it has the mid-length gas system so that subscribers to that particular voodoo can check off their internet boxes.

But I'd be just as interested if it was simply a 6720 being sold with a Ceturion MLOK handguard.

Some of the pictures I see of this gun scare me though as they seem to have a bunch of "ambi" uselessness on them, which I suppose also addresses market demand and Internet checkboxes.

Actually, a lot of Ambi is because of the military and their solicitations, which people follow online.

Midlength is a proven concept in the real-world.

[rob_s]

Colt should just really name this thing the "Colt intent model, because:theory" and be done.

Any news on when it's coming out?

[MistWolf]

You must be an engineer.

The "advantages" you mention are theoretical until tested, and irrelevant until shown to have an impact on performance. "Gas cutting" is right up there with "dwell time", as far as I'm concerned.

But in any case, I'm still interested in this gun, as I think it makes a viable "first AR" suggestion (pending details, price point, etc.), in part because it has the mid-length gas system so that subscribers to that particular voodoo can check off their internet boxes.

But I'd be just as interested if it was simply a 6720 being sold with a Ceturion MLOK handguard.

Some of the pictures I see of this gun scare me though as they seem to have a bunch of "ambi" uselessness on them, which I suppose also addresses market demand and Internet checkboxes.

I am a licensed Aviation Airframe and Powerplant Technician. I deal with a variety of aircraft systems and have to know the principles that make them work.

Rob, you said "become your own SME", so that's what I did. I began studying how an AR works, applying scientific principles and physics instead of relying on what was being bandied about on the internet. It's been an interesting journey. While you may not understand these principles, that doesn't make it voodoo. The differences between the carbine and the middy are small but that does not mean they are only desirable to the unwashed masses of dirt clod shooters.

The advantages of the middie that I talked about are not theoretical. They are. The differences are not a large one, such as going from a 5 round fixed magazine to a 20 round detachable magazine, or going from a bolt action to a gas operated self loading rifle. But that doesn't make them any less real. Whether or not the advantages are enough for an individual to choose one over the other is up to that individual. Just like ambi controls. In fact, the Army is in the process of upgrading their M4s, including the addition of an ambidextrous safety. The ambi safety is going to become the new standard.

When someone's arguments are derisive, resort to name calling and dismiss the facts, their opinion loses authority.

Unobtanium, dwell time as defined in my earlier post, hasn't any effect on the function of a gas operated rifle. The difference in "dwell time" between a 14.5 inch and a 16 inch barrel is about .05 milliseconds. That's not enough time to make a difference under the circumstances. But the extra length does mean it takes more time for the barrel to vent after the bullet has exited

[rob_s]

I am a licensed Aviation Airframe and Powerplant Technician. I deal with a variety of aircraft systems and have to know the principles that make them work.

Rob, you said "become your own SME", so that's what I did. I began studying how an AR works, applying scientific principles and physics instead of relying on what was being bandied about on the internet. It's been an interesting journey. While you may not understand these principles, that doesn't make it voodoo. The differences between the carbine and the middy are small but that does not mean they are only desirable to the unwashed masses of dirt clod shooters.

The advantages of the middie that I talked about are not theoretical. They are. The differences are not a large one, such as going from a 5 round fixed magazine to a 20 round detachable magazine, or going from a bolt action to a gas operated self loading rifle. But that doesn't make them any less real. Whether or not the advantages are enough for an individual to choose one over the other is up to that individual. Just like ambi controls. In fact, the Army is in the process of upgrading their M4s, including the addition of an ambidextrous safety. The ambi safety is going to become the new standard.

When someone's arguments are derisive, resort to name calling and dismiss the facts, their opinion loses authority.

Unobtanium, dwell time as defined in my earlier post, hasn't any effect on the function of a gas operated rifle. The difference in "dwell time" between a 14.5 inch and a 16 inch barrel is about .05 milliseconds. That's not enough time to make a difference under the circumstances. But the extra length does mean it takes more time for the barrel to vent after the bullet has exited

I don't think you understand my point.

All of the advantages you talk about are theoretical until such time as they are proven to affect performance that actually matters.

People talk about gas cutting, dwell time, etc. and it's all just internet jargon being bandied about if it can't be proven to benefit
1) accuracy
2) reliability
3) durability
4) time between hits
etc.

Unless you have studies that the various gas-flow issues affect measurable performance gains, they aren't, as far as I'm concerned.

I don't think it's voodoo, I think it's irrelevant, and un-proven to actually matter in any meaningful way.

Specifically, you mention reduced "gas cutting" as an alleged benefit. you may have mentioned others, but that's the only one I've picked up. How much less? as measured against what? What is the sample size of the test? What is the meaningful benefit to the end user? If it's a longevity issue, what's the delta between the legacy system and the new hotness?

[breakingtime91]

Rob, I am no expert but from shooting a stock colt 6920 side by side with a bcm midlength the midlength shot much flatter. Both with A2 flash hiders. Not sure what your qualifications are (don't mean that in a snarky way) but from a non bias view, I will pick a midlength. With that said I have a soft spot in my heart for a true M4 carbine.

[rob_s]

Rob, I am no expert but from shooting a stock colt 6920 side by side with a bcm midlength the midlength shot much flatter. Both with A2 flash hiders. Not sure what your qualifications are (don't mean that in a snarky way) but from a non bias view, I will pick a midlength. With that said I have a soft spot in my heart for a true M4 carbine.

This is kind of my point.

I think it may help to think of things in a micro vs. macro scale.

Micro scale would be things going on inside the gun, macro would be the results outside the gun. Or call it "internal" vs. "external". To put it in car terms, HP would be internal, 1/4 mile time would be external. I understand all the theories about gas this and flat that, but I want to know how it helps my 1/4 mile time.

So your 6920 vs. midlength is a great comparison, albeit missing a lot of relevant information. First, was the 6920 stock, and what was the exact configuration of the mid-length? Second, what was the measured benefit of the "flatter" gun (more accurate, faster shots, quicker target transitions, etc.)?

See, qualifications or no, I can hand you two guns, one a mid-length and one a carbine-length, and if my goal is to make you choose one vs. the other because:recoil I can rig the guns to make you choose one over the other. If you want faster split-times, I can rig the guns to make you choose the one I want.

Specific to your mentioned benefit of "flatter shooting", and ignoring the muzzle device because you said "both with A2", we can change elements inside the stock, inside the upper, and inside the handguards (among other things) to affect that characteristic.

[orionz06]

So if the mid length isn't worse then what's the big fucking deal?


Sent from my Nokia 3310 using an owl

[rob_s]

So if the mid length isn't worse then what's the big fucking deal?

nothing really, other than why change something for no benefit?

Or, more particularly, I often see people recommend a new buyer go order parts and pieces from all over God's creation instead of just buying a stock gun all at once just to "get the benefits of the mid-length".

I've been hearing that the mid-length is "better" since Armalite first started pimping it, and I've been waiting around to have someone explain the tangible, performance, benefit ever since. People get so adamant about it I mistakenly assume they have something beyond theory and feel.

Reminds me a lot of the K&N air filter guys.

[orionz06]

If the hypothetical customer doesn't have a gun it's not a change, it's just a different gun that has nothing wrong with it. Unless you don't want them to have a mid length....


K&N did provide a benefit but also had drawbacks that included allowing shit into the intake.


Sent from my Nokia 3310 using an owl

[rob_s]

If the hypothetical customer doesn't have a gun it's not a change, it's just a different gun that has nothing wrong with it. Unless you don't want them to have a mid length....
I don't really care what they buy, I'm just surprised that all the people hollering "get a midlength!" don't have any real reason for it.



K&N did provide a benefit but also had drawbacks that included allowing shit into the intake.
I'm talking more about the "I put a K&N on my car and could feel the 10 HP gain" crowd.

[orionz06]

I don't really care what they buy, I'm just surprised that all the people hollering "get a midlength!" don't have any real reason for it.



I'm talking more about the "I put a K&N on my car and could feel the 10 HP gain" crowd.

You've dismissed the reasons.


Oh, those people...


Sent from my Nokia 3310 using an owl

[rob_s]

You've dismissed the reasons.

Really?

In that case, maybe someone should just list them, perhaps in order of importance or significance, because I haven't seen a single tangible performance "reason". Try to keep it simple, since I clearly don't understand. It would probably be helpful to all the other dumb people that don't understand if maybe there was a list of the reasons and benefits. If the "reasons" require long drawn out explanations, maybe it would be good to go with a bullet-point type list. Something like this.

(1) Short Description of reason/benefit one
(a) long-winded engineering explanation of how and why it matters
(b) case-studies measuring tangible benefit (with links, if possible)

(2) Short Description of reason/benefit two
(a) long-winded engineering explanation of how and why it matters
(b) case-studies measuring tangible benefit (with links, if possible)

(3) Short Description of reason/benefit three
(a) long-winded engineering explanation of how and why it matters
(b) case-studies measuring tangible benefit (with links, if possible)

[breakingtime91]

This is kind of my point.

I think it may help to think of things in a micro vs. macro scale.

Micro scale would be things going on inside the gun, macro would be the results outside the gun. Or call it "internal" vs. "external". To put it in car terms, HP would be internal, 1/4 mile time would be external. I understand all the theories about gas this and flat that, but I want to know how it helps my 1/4 mile time.

So your 6920 vs. midlength is a great comparison, albeit missing a lot of relevant information. First, was the 6920 stock, and what was the exact configuration of the mid-length? Second, what was the measured benefit of the "flatter" gun (more accurate, faster shots, quicker target transitions, etc.)?

See, qualifications or no, I can hand you two guns, one a mid-length and one a carbine-length, and if my goal is to make you choose one vs. the other because:recoil I can rig the guns to make you choose one over the other. If you want faster split-times, I can rig the guns to make you choose the one I want.

Specific to your mentioned benefit of "flatter shooting", and ignoring the muzzle device because you said "both with A2", we can change elements inside the stock, inside the upper, and inside the handguards (among other things) to affect that characteristic.

ok Rob so I gave you the answer in my initial sentence. both were stock with A2 flash hiders. Bcm midlength had a kmr rail like a lot of the "standard stock" Bcm Middies do. Yes midlength was more accurate when shooting quickly during a Marine Corps Marsoc rifle qualification (I use this as a benchmark). Both guns, from their factories, stock with red dots. Make your own conclusions Rob because apparently my explanation isn't going with your rhetoric.

[rob_s]

I wonder if we could persuade a mod to break this thread up?

While I enjoy the mid-length discussion, at this point there's maybe 5 posts in the thread having to do with the new Colt which was the purpose of the thread to begin with, and my purpose for resurrecting it. Would be nice to separate the two.

[rob_s]

ok Rob so I gave you the answer in my initial sentence. both were stock with A2 flash hiders. Bcm midlength had a kmr rail like a lot of the "standard stock" Bcm Middies do. Yes midlength was more accurate when shooting quickly during a Marine Corps Marsoc rifle qualification (I use this as a benchmark). Both guns, from their factories, stock with red dots. Make your own conclusions Rob because apparently my explanation isn't going with your rhetoric.

It's only "rhetoric" because you don't seem to like being questioned.

how much more accurate? What is your measure of accuracy? What is the target used? This is a scored test, yes? What was the score with either gun?

[TGS]

Buying midlengths makes Rob_s mad and storm about what portions of the interwebs haven't banned him yet.

That's not tangible, but that's certainly a benefit worth buying the midlength for.

[MistWolf]

Specifically, you mention reduced "gas cutting" as an alleged benefit. you may have mentioned others, but that's the only one I've picked up

So, you didn't read all of my post.

In the grand scheme of things, it's not necessary to guide a beginning shooter to a middy. Or to a free float tube, aftermarket furniture or a replacement trigger. But if you don't understand the real benefits, downsides and compromises of each choice, how can you explain to anyone why or why not they should make that choice? Or whether or not that choice is important? You can't just tell someone "the advantages of a middy are irrelevant" any more than you can just tell them "because dwell time". Your argument that it's all theory because there are no numbers is invalid. If you were to say "We do not know how much advantage the middy has over the carbine gas system without measurements", you would be correct. But we know there is an advantage because of the laws of physics and it can be measured. Instead of waiting for somebody to prove it to you, look into it for yourself. Ball is in your court. Do with it what you will

[Unobtanium]

Really?

In that case, maybe someone should just list them, perhaps in order of importance or significance, because I haven't seen a single tangible performance "reason". Try to keep it simple, since I clearly don't understand. It would probably be helpful to all the other dumb people that don't understand if maybe there was a list of the reasons and benefits. If the "reasons" require long drawn out explanations, maybe it would be good to go with a bullet-point type list. Something like this.

(1) Short Description of reason/benefit one Less port erosion, and thus less cyclic rate change during the life of the barrel.
(a) long-winded engineering explanation of how and why it matters Less need to re-tune the rifle to prevent it from outrunning magazines suppressed (or not, in extreme cases), etc. via playing musical buffers during the life of the barrel.
(b) case-studies measuring tangible benefit (with links, if possible) I don't think I need to provide a link to explain to you that the further from the chamber, the less pressure the gas which escapes out of the gas port has, nor should I have to explain that less pressure = less erosion of the orifice that the hot gas and particulate is blasting out of. If you disagree, and cannot understand, I will break it down reverse-Barney-style with some tech-heavy links.

(2) Short Description of reason/benefit two The further from the BCG the gas-port is, the more volume is in the tube, the further it has to travel, the longer the lock-time is before unlocking occurs, and the less pressure residual is in the barrel, resulting in easier extraction of the case.
(a) long-winded engineering explanation of how and why it matters Less pressure in the barrel equals easier extraction, and if you didn't already know, the extractor assembly of the M4/M16 is not the most robust in the world. It was designed for the M16 with rifle-length gas system, and its geometry has not been changed since.
(b) case-studies measuring tangible benefit (with links, if possible) The original M16 spring was replaced with a 5-coil spring/buffer ring, etc. when the gas port was moved nearer the chamber in the M4 carbine, due to FTE issues. Again, do I really need links, here?

(3) Short Description of reason/benefit three The middy has less recoil and still maintains function, all things equal.
(a) long-winded engineering explanation of how and why it matters This comes down to peak pressures, timing, and impulses. It should be obvious. If not, shoot an A2/4, then shoot a 6920.
(b) case-studies measuring tangible benefit (with links, if possible)

Your game is stupid, but I played.

[John Hearne]

Not an engineer but I would have sworn that Uncle Pat reported bolt lugs breaking at much longer intervals with middy guns. Am I hallucinating again?

[orionz06]

Not an engineer but I would have sworn that Uncle Pat reported bolt lugs breaking at much longer intervals with middy guns. Am I hallucinating again?

That would make sense, you know, matching theory and all...

[Unobtanium]

Not an engineer but I would have sworn that Uncle Pat reported bolt lugs breaking at much longer intervals with middy guns. Am I hallucinating again?

Well, we all know that rifles break lugs at the same rate that carbines do...oh wait...no they don't. Well what's different about a rifle vs. a carbine? Hmmm...I think you're onto something...

[BWT]

Not an engineer but I would have sworn that Uncle Pat reported bolt lugs breaking at much longer intervals with middy guns. Am I hallucinating again?

I know he ran Filthy 14 to 16,000 rounds before two lugs broke, and then he ran it out to almost 29,000 with the replacement BCG.

I know Pat ran a lot of guns and tracked that, but I don't have carbine numbers from him.

http://www.slip2000.com/blog/s-w-a-t-magazine-filthy-14/


At Brady, Texas, in March 2009, it suffered a malfunction, which was reduced with Immediate Action. The bolt was wiped down at 6,450 rounds.

At Prairie du Chien, Wisconsin, in May 2009, it had several failures to extract, and the extractor spring was replaced at 13,010 rounds. This is far beyond the normal extractor spring life under these conditions.

At Wamego, Kansas, in June 2009, two bolt lugs broke at 16,400 rounds. We replaced the BCG. Considering the firing schedule, this is within normal parameters.

At Columbus, Ohio, in November 2009, we had several failures to extract at 24,450 rounds. The shooter gave it a field cleaning and replaced the extractor and extractor spring.

At 28,905 rounds, we finally cleaned Filthy 14. As part of our year-end maintenance schedule, we inspect and replace parts as necessary. Filthy 14 looked like the inside of the crankcase of Uncle Ed’s ’49 Packard. It was disgusting to look at and contaminated everything near it, somewhat like the toner cartridges for old printers.

I plopped it into a parts washer filled with Slip 725 parts cleaner, and 20 minutes later it was clean. Mostly clean, anyway.

We have never used a bore brush in the barrel of this gun. We did run a patch down the barrel twice, but that was all. At 50 yards it still shoots two-inch groups, and we understand that it might not at 100 yards and beyond, but we are happy with the fact that, even at 50 yards, the gun is capable of tighter groups than most of the people running it.

Could the longer than normal extractor, extractor springs, BCG, and retention of accuracy have to do with the Mid-Length?

Potentially.

Common knowledge to me was bolts at 7,500.

I know I have my Mid-Length BCM has approximately 8,000-10,000 rounds of predominantly Wolf, Tula, and probably 100-150 rounds of actual brass case 5.56x45mm. Green GI followers and the AR system in conjunction with the heaviest buffer they may for it (A5H2) have caused the maybe three malfunctions in the gun.

Any long term statistics on Carbine guns and bolts?

God Bless,

Brandon

ETA: I don't know that the accuracy retention would be affected by how little or how much a gas port was eroded. So, that may just be a function of a properly made 11595E compliant Barrel. It definitely makes you wonder how necessary a Cold Hammer Forged barrel is.

[Unobtanium]

But then, a bunch if colt 6920s are on the line at battlefield Las vegas, round counts were over 60k when the bolts popped...

[mmc45414]

Isn't carbine gas length on a 16" deviation too?
Yes, but, wasn't the 20" the deviation from the USAF request in the first place?:)

[Casual Friday]

I've decided to nickname my 14.5" mid length "rob_s' spirit animal" in honor of this thread.

[BWT]

But then, a bunch if colt 6920s are on the line at battlefield Las vegas, round counts were over 60k when the bolts popped...

Any citation for that?

The Govt. isn't know for replacing parts 10-15% of the way into their service life from what I've gathered.

I'm slightly skeptical.

God Bless,

Brandon

[SecondsCount]

Your game is stupid, but I played.

Your explanation was clear and is pretty much how I understood the benefits of the midlength system to be.


Any citation for that?

The Govt. isn't know for replacing parts 10-15% of the way into their service life from what I've gathered.

I'm slightly skeptical.

God Bless,

Brandon

I am skeptical as well although they could be running some lower pressure 223 ammo that is easier on the gun but I would think a barrel would be pretty shot out by then, actually well before then. At 20,000 rounds the throat on that carbine has probably moved several inches out.

[BWT]

Also, I'm not planning on provoking anything.

I just looked quickly at the percentile and if the recommended BCG (or bolt) replacement in an M4A1 is 7,500. 7,500 is 12.5% of 60,000 rounds.

The extractors alone would almost certainly need to be replaced at least once. If not the action spring and other components.

I have a personal Midlength BCM go without a replacement of Bolt, Carry, Extractor, Action Spring or anything at about 8,000-10,000 rounds.

That's also weak steel cased ammo.

Food for thought.

God Bless,

Brandon

... That being said I probably need to replace the extractor, spring, insert, and action spring once I wrap up this semester in early August.

[John Hearne]

I am skeptical as well although they could be running some lower pressure 223 ammo that is easier on the gun but I would think a barrel would be pretty shot out by then, actually well before then. At 20,000 rounds the throat on that carbine has probably moved several inches out.

I had the same thoughts about ammo pressure but I'm not sure Uncle Pat ran 5.56 spec ammo for every round - I could be wrong.

Regarding the Battlefield data they were very honest that throat erosion and accuracy was never a concern for their customers.

[BWT]

I had the same thoughts about ammo pressure but I'm not sure Uncle Pat ran 5.56 spec ammo for every round - I could be wrong.

Regarding the Battlefield data they were very honest that throat erosion and accuracy was never a concern for their customers.

I would think that barrel life would be gone for sure. However, Pat's test had two replacement extractors and one replacement bolt (with two broken lugs).

If that was a loaner gun for training (I had the impression that might be part of the situation); he may've had guys shooting Mil-Spec pressure 5.56.

The Midlength gun in Pat's test was able to maintain a 2'' group at 50 yards post-test (at about 29,000 rounds).

Hard to say for certain. I was just stunned that the gun was failing to extract at 13,000 and they replaced the spring, sheered two lugs at 16,000 and replaced the BCG, and replaced the extractor and extractor spring at 24,000.

It seems at about 10,000-ish rounds expect an extractor spring/extractor to need to be replaced.

God Bless,

Brandon

I plan to shoot my Midlength until something breaks in regards to components; I will replace the springs/inserts though. I figure broken bolt lugs or extractor are easy enough.

I would be surprised if I ever truly shot out the barrel because it's taken me 7 years to get to this point and a large part of that was when I was a Bachelor.

Who knows.

[Malamute]

Any citation for that?


I'm slightly skeptical.

God Bless,

Brandon

The guy that owns BFLV posted on one or two of the forums, it may have been linked from another one,...or something. He discussed several aspects of the rental guns, and what ammo they were using (think he mentioned they were buying it by truckloads or something crazy on conrtacts). I think the round count for them was just run them til they broke and replace parts as needed. The barrel condition didnt matter that much. If the throat was washed out some, it wasnt a huge issue. The range was relatively short, they shot OK for a rental gun that most people shot full auto anyway. I think he said the basic upper and lower receivers were functionally fine til 200K rounds. That's assuming replacing anything that wore out or broke along the way.

Was interesting reading on the forum link (arf), until it got shat on by petty bickering about peoples pet ideas.

ETA:1 Hey look,

http://www.thefirearmblog.com/blog/2015/09/08/ar-endurance-findings-at-a-rental-range/

ETA:2 Interesting "...Also, the gas port holes erode away much faster on the shorties"

ETA:3 gleaned from the chaff of the forum "The 20" weapons get used daily but only about a fifth of the time as the shorter barreled units. I'll have to check the maintenance logs but I don't believe we've lost any bolts, carriers or any other major components in one of them."

[Sero Sed Serio]

I'm pretty sure that BFLV's accuracy standards are not keyholing at 7 yards or something like that...there's a lot of great data about high round counts coming out of there, but considering their average user shoots minute-of-Vegas-strip groups, I can see why barrel life info might be a bit skewed.

[Malamute]

I'm pretty sure that BFLV's accuracy standards are not keyholing at 7 yards or something like that...there's a lot of great data about high round counts coming out of there, but considering their average user shoots minute-of-Vegas-strip groups, I can see why barrel life info might be a bit skewed.

Yes, that definitely has to be taken into consideration. The interesting parts are the basic functioning of the guns.

15 yards I believe.

[Unobtanium]

Any citation for that?

The Govt. isn't know for replacing parts 10-15% of the way into their service life from what I've gathered.

I'm slightly skeptical.

God Bless,

Brandon
Yes, the owner of Battle Field Las Vegas himself has posted about it extensively. Their accuracy standards are very low, though. Basically, if it doesn't keyhole , it's gravy. They are in the business of making money, and customers are happy as long as they can hit the target. Here is the quote regarding Colt Bolts, and a quote about those weapons in particular.


The Colt bolts were WELL past the 60,000 round count before suffering a sheared lug. As for LaRue's, we don't have any of them on the line. Also, we still have plenty of other Colt's we put on the line that the bolts are still fine and headspace is within spec'.

V/R
Ron

As pertains to another weapon (not the Colts in question), relating to their "accuracy standards":

The weapon started to keyhole so it was pulled from the line. We can't take the chance of a round coming back from the round going down range like that.

V/R
Ron

This was posted about one of the relevant Colt's on 5/10/16:

On a side note, we lost a key on one of the Colt M4's that went on the line back in October or November I believe. That rifle has some HIGH mileage and the carrier lasted a LONG time.

This is him discussing bolt-life, in general:

I would have to say that AK has a slight edge over the M4. The M4 bolts won't last as long as the AK bolt but the receivers on M4's can go over 200,000 rounds as compared to the 100,000 rounds (on average) on a stamped AK receiver. The reason I say slight edge is because most people will never get to the 100,000 round count on their weapon so losing a bolt in your M4 in the 30,000-50,000 round count range is the deciding factor for me.

V/R
Ron

This might give you a clue as to how those Colt's are abused...

We removed all the factory hammers, triggers and disconnectors and replaced them with JT Distributing M16 parts and sold them off as a lot. I couldn't tell you if there were any issues or not but these were new productions rifles that had just been delivered from the factory.

V/R
Ron

A bit more info on the Colts:


Quite a few of you have asked about how the Colt M4's are holding up since being put on the line (according to our records, this particular rifle went on the line 02 OCT 15). They have handled very well with no broken bolts, no broken hammer/trigger pins, no eroded gas tubes or any other failures up until this week. I do want to put it out there that the RSO's really like these weapons. They were all outfitted with the exact same Magpul furniture in two different colors to help in swapping out weekly. They all have MOE handguards with a forward pistol grip to help control heat issues. These weapons get hot after several magazines and when you have parties of anywhere from 2-20 people shooting, the weapons are intolerable for the person who's never handled a firearm to enjoy the experience.

That being said, the RSO's have used these weapons every day of the week and migrate towards the Colt's. They have been on the line since the first week of October and as stated above, they haven't suffered from any issues up until this point. The only reason that I am bringing this up is because I was in the armory yesterday morning and I noticed on of the Colt's disassembled on the bench. It was a FDE model and I knew that those models were on the line and shouldn't be down for cleaning. I asked my armorer Danny Boy what the issue was and he said that the ejector spring was in about 7-8 pieces and that it actually happened to be the second one of the morning. I thought that was pretty odd for two ejector springs to go out in the same day. My other armorer Sean stated that he had already replaced two others early this week for a total of four Colt M4's to suffer ejector spring failure in one week. Also, the ejector pin spring sheared upon failure and had to be punched out.

For this rifle to have four HARD months of use and only suffer from a ejector spring failure is really good in my opinion but the fact that four went down with the exact same issue is what's strange. Also, we never saw the usual slow down during the November through February season and these weapons have continued to see high round counts. Without looking at numbers of rounds consumed for the time period it's fair to see these rifles have no less than 25,000-30,000 rounds through them.

Today is my day off but I will send a message to the armorers to go ahead replace all the ejector springs in the Colt M4's as preventive maintenance and to avoid malfunctions with customers on the range.

V/R
Ron
http://i.imgur.com/8GfpeLe.jpg
http://i.imgur.com/8gyO3wG.jpg




Anyway, these guys RUN A GUN HARD, if you can't figure that out from the quotes above and checking out the time-line of when those guns came on line until they had tens of thousands through 'em. Bet you haven't seen this before:

http://i.imgur.com/AVVXqNY.jpg
http://i.imgur.com/R0nWZm0.jpg
http://i.imgur.com/N59gdEO.jpg

I've previously stated that we've never lost a AR15 receiver due to wear like we have with AK's. Well, with over three years of constant use that is no longer the truth. It's very clear how deep the bolt carrier key has worn into the upper receiver over the years. The armorers made notes in their records about the wear pattern but didn't see a need to replace the receiver as it continued to function and barrels had been swapped (making sure the headspace was kept in spec) with no issue of reliability.

The weapon came off the line because the RSO stated that the bolt wouldn't go into battery. Initially they assumed there must have been a sheared key or case inside the barrel extension area that wouldn't allow the bolt to close. After further inspection, they noticed that the bolt was hitting the face of the barrel extension. They stripped the weapon down and that's when they discovered that there had been so much wear that the bolt carrier was being pushed upward and causing the misalignment. To go back and do the math on the round count would take a VERY long time and even then it would only be good estimate. What I do know is that this particular rifle was one of mine before we opened Battlefield Vegas and has been on the line since day one. It's had two barrel swaps, several bolt's and numerous springs, extractors, etc but it was a great running gun and that's why they kept it on the line. I don't remember who I purchased this receiver from but it's fair to say that it wasn't a high-dollar upper by any means. This was a personal weapon that we used for demo's and I couldn't afford a nice rifle to let LE use and abuse so more than likely it was from JT Distributing or DS Arms.

We had distributor accounts set up with both of them prior to opening Battlefield and used quite a bit of their products. Either way, it's a standard forged upper receiver that has lasted untold thousands of rounds before failing. I don't want people to come out and say that I am stretching the truth but I will throw some numbers out there and let you do the math. Each M4 on the line will get a minimum of 20 magazines run through it each day and each magazine has 25 rounds. Just for fun, let's just say that it was on the line only 3 out of the 7 days of week for 3 years and 3 months. Now, that is a very conservative number because there are SO many times that we go through 10,000+ rounds of .223 on a Saturday in the last three years.

Here are some pics...

[rob_s]

Your game is stupid, but I played.

Stupid games for stupid people.

Not one citation, not one quantification, not one anything of value.

[rob_s]

So, you didn't read all of my post.

In the grand scheme of things, it's not necessary to guide a beginning shooter to a middy. Or to a free float tube, aftermarket furniture or a replacement trigger. But if you don't understand the real benefits, downsides and compromises of each choice, how can you explain to anyone why or why not they should make that choice? Or whether or not that choice is important? You can't just tell someone "the advantages of a middy are irrelevant" any more than you can just tell them "because dwell time". Your argument that it's all theory because there are no numbers is invalid. If you were to say "We do not know how much advantage the middy has over the carbine gas system without measurements", you would be correct. But we know there is an advantage because of the laws of physics and it can be measured. Instead of waiting for somebody to prove it to you, look into it for yourself. Ball is in your court. Do with it what you will

What seems to be bothering you is that I have read everything you posted, you haven't posted anything I didn't already know or haven't heard before, I do understand the concepts, and I see no "real benefits".

The ball hasn't been in my court from the get go, because nobody can prove a tangible be fit to any of this nonsense. No documented cases of prolonged life, no documented numbers to show improved scores on any test by any meaningful number of shooters, no nothing.

It really is the K$N air filter thing all over again. Everyone agrees more airflow is theoretically "better" but nobody can document how much better or how that theoretical "better" benefits the user.

[rob_s]

Buying midlengths makes Rob_s mad and storm about what portions of the interwebs haven't banned him yet.

That's not tangible, but that's certainly a benefit worth buying the midlength for.

I'm not mad, I'm amused. Even the people that identify this as a game can't resist coming in and rambling on about nothing, with no documentation to support their rambling.

This is entertainment for me. I'm still shooting two 6933s and a flattop conversion 6720 (since the time when you could only buy them with an A2 upper) that the people have been telling me are in accurate, are going to fail, etc. since the ban expired. For many of those years I was shooting upwards of 8-10k rounds a year, with the 6720 getting most of the abuse (outside of T&E and loaner guns), and yet it's still here chugging along.

I chased "better" that entire time, and still come back to that 6720, almost unchanged since the day I swapped the upper and chopped the FSB.

[Unobtanium]

I'm not mad, I'm amused. Even the people that identify this as a game can't resist coming in and rambling on about nothing, with no documentation to support their rambling.

This is entertainment for me. I'm still shooting two 6933s and a flattop conversion 6720 (since the time when you could only buy them with an A2 upper) that the people have been telling me are in accurate, are going to fail, etc. since the ban expired. For many of those years I was shooting upwards of 8-10k rounds a year, with the 6720 getting most of the abuse (outside of T&E and loaner guns), and yet it's still here chugging along.

I chased "better" that entire time, and still come back to that 6720, almost unchanged since the day I swapped the upper and chopped the FSB.

Can you provide documentation that chopping the fsb is a good idea? Seriously, everything from accelerometer data to gas port erosion measurements exist. You just want to believe what you want to believe...and that's absolutely ok.

[jeep45238]

The thing I love about this, is rob_s is demanding citations for technical studies that requires very specialized equipment that none of us has, and purports that because we don't immediately have this information that it therefore can't be true (never mind physics, theories, scientific methods, real world experiences). However, he hasn't provided any of the same evidence he demands to counter any arguments made.

Benefits change based off of context, and advantages are fractional - but to blatantly claim that things are more or less b.s. and hold double standards is contrary to having solid discussions in search of the truth. Disagreements are what breeds insights, discussion, and education but only if both sides act like adults.

[breakingtime91]

Rob you either troll really well or your just an ass.

[Luke]

I wanna hang out with Rob. He's either pretty cool or a douche bag and I don't think we will ever know until there is real life interaction.

[SecondsCount]

I wanna hang out with Rob. He's either pretty cool or a douche bag and I don't think we will ever know until there is real life interaction.

I met Rob once down at Markham Park and we had a friendly conversation but I could not get him to show me his Colt tattoo ;) What I like about him is that he doesn't get all caught up in the whizbang stuff and is a KISS kind of guy. If he is happy with the carbine length system then it's all good but after a couple issues with carbine length, non-Colt guns, I moved on to midlength and have not had an issue since.

[Gadfly]

Reading through all of this, I keep seeing the theme of no one can prove "mid length helps with X,Y,Z"...

Flipping that around, what does a mid length hurt? Any documentation of Mid length being a problem?


(I say this as a guy with 4 personally owned carbine length systems, and armoring carbine gas systems for 200 agents. No issues.)

[orionz06]

Reading through all of this, I keep seeing the theme of no one can prove "mid length helps with X,Y,Z"...

Flipping that around, what does a mid length hurt? Any documentation of Mid length being a problem?


(I say this as a guy with 4 personally owned carbine length systems, and armoring carbine gas systems for 200 agents. No issues.)

I already asked this.


Sent from my Nokia 3310 using an owl

[Gadfly]

I already asked this.


Sent from my Nokia 3310 using an owl

I saw that. I read his replies over the past few days.

I was more asking Specific Problems/ failures caused by any mid length. (Other than his "its just marketing gimmicks...different just to be different..blah blah...no noticeable advantage...blah blah".")

[BWT]

Reading through all of this, I keep seeing the theme of no one can prove "mid length helps with X,Y,Z"...

Flipping that around, what does a mid length hurt? Any documentation of Mid length being a problem?


(I say this as a guy with 4 personally owned carbine length systems, and armoring carbine gas systems for 200 agents. No issues.)

The only times I've seen consistent issues with Midlength system was when the barrel was right on the edge of what made it too short. For instance, 14.5'' Mid-Lengths need 5.56mm or at least a full bodied .223 Rem from what I've gleaned online. 10.5'' SBR's are probably the most finicky barrel length in a carbine gas system.

When I see threads on questionable reliability related to gas systems or being ammo sensitive. It's usually those kind of issues.

I've mentioned here several times (in several threads) my experience, and from what I've seen from others with Mid Length gas systems; it's generally very reliable. I have both gas systems and the only actual malfunction I've ever had in either was a Failure To Extract in a Midlength 16'' with a Sionics lower with an A5 system with an A5H2 buffer with Independence ammo.

That concerned me so much; I bought a BCM lower with a Carbine RE and H buffer afterwards as the lower I wanted to register as an SBR prior to 41P. I had not ever seen that error before. I took that lower to the range and ran probably 60-80 rounds through it with the Midlength upper and decided it was worthy to register.

To Unobtanium, thank you for all of the information you posted. I'm stunned to see Colts still running with that many rounds. .223 or not, that's insane.

As far as rob_s, you act like you have never shot a BCM Midlength or used BCMs extensively but I find that funny because you were part of the group that had BCM weapons.

You were influential on me in going to a BCM Midlength in 2009 when I did. If you google rob_s and BCM I find you associated with BCM dissipater projects or midlength guns, etc. (http://www.m4carbine.net/archive/index.php/t-80877.html) dating back over half a decade.

What happened with your association to BCM and now sole devotion to Colt?

You seem to always have liked Colt and fair enough they make great stuff.

I'm just scratching my head on the "Mid Length is unnecessary" and amusement on behalf of other members stuff.

I'll admit I've poked and prodded back. I certainly didn't have to insinuate that Midlength AR's would get you killed on the street. But, I figured have fun rather than these types of conversations.

Maybe Midlength is just the thing that draws your ire these days.

God Bless,

Brandon

ETA: Also, I saw that with the intermediate gas system on SR-15's in a 16'' barrel seemed to have reliability issues as well with lower velocity steel cased ammo. KAC remedied that with larger gas ports I believe.

[Unobtanium]

Stupid games for stupid people.

Not one citation, not one quantification, not one anything of value.



If you can't understand that gas at 32,900psi will erode the orifice it is flowing through sooner than gas at 26,500psi, I'm not sure that ANYTHING is going to help you see any merits. More succinctly, I think you choose not to see any merits, much like I know a few people who think their M14 can do anything your M4 can do, except with 1500# more energy.

[jeep45238]

If you can't understand that gas at 32,900psi will erode the orifice it is flowing through sooner than gas at 26,500psi, I'm not sure that ANYTHING is going to help you see any merits. More succinctly, I think you choose not to see any merits, much like I know a few people who think their M14 can do anything your M4 can do, except with 1500# more energy.



Don't worry, he hasn't provided one citation, one quantification, or anything of value. Some people can't understand that gas can (and does) erode a solid material.

[farscott]

As an engineer, I see the qualitative benefits of the mid-length system, but I also see that there is data that proves the carbine-length gas system is sufficient for the 14.5"-barreled M4. There are a ton of units in the field that show the carbine-length system is good enough for most applications. There is also some data that suggests that the carbine-length gas system is not sufficient for extended round counts at high firing rates as seen in some battles in Afghanistan. The data does not exist for the mid-length gas system. I can see that lower-pressure gas for longer barrel lengths stresses the gas tube and the BCG less, but there is no data that quantifies an improvement in component or system life. There is anecdotal data that says BCGs last longer in mid-length gas guns and the gas tubes should erode less, but there are not nearly as many guns in the field with known track records as there are M4 carbine-length rifles. Mid-length makes intuitive sense, but the validation test data is not extant.

That being said, there are reasons to use mid-length gas systems that make sense for barrel-lengths longer than 14.5". As someone who uses barrels from 16" to 18", I like mid-length gas systems. They work for my needs for those guns. I also have a Colt 6920.

[orionz06]

I'm not sure the argument was ever for a 14.5" middy but rather having the tube length move with the barrel length... Carbine up to 14.5, middy at 16, rifle at 20, and then 18 is the middle ground.

[JAD]

In other threads that completely duplicate this one in content, SLG mentioned several issues with midlengths and expressed concern that they were unproven. Ain't none of you said anything that makes me think you know a lot more than SLG about high round count ARs.

[Luke]

In other threads that completely duplicate this one in content, SLG mentioned several issues with midlengths and expressed concern that they were unproven. Ain't none of you said anything that makes me think you know a lot more than SLG about high round count ARs.

Did he say what problems he saw and how many rifles had problems? Got a linky?

[farscott]

In other threads that completely duplicate this one in content, SLG mentioned several issues with midlengths and expressed concern that they were unproven. Ain't none of you said anything that makes me think you know a lot more than SLG about high round count ARs.

That is a much more succinct version of what I was trying to state: There is no data that proves the mid-length is suitable as there is for the carbine-length gas system.

[orionz06]

Is there even anecdotal evidence that mid lengths don't work? Remember... Rifle length does work and is proven.


Sent from my Nokia 3310 using an owl

[breakingtime91]

In other threads that completely duplicate this one in content, SLG mentioned several issues with midlengths and expressed concern that they were unproven. Ain't none of you said anything that makes me think you know a lot more than SLG about high round count ARs.

I remember him specifying 14.5 mid-lengths run on the edge of reliable and that carbines are more proven. I understand what your trying to do, but no one is saying carbine sucks. They are just saying there are benefits to mid-length. Not to be a jerk but this reminds me of when our unit switched from m16a4 to M4 and people were non stop bashing on them for being less lethal, less proven, and less reliable. So if we want to go off those guys logic JAD, guys who had a lot of trigger time behind AR pattern rifles, we would all be running around with m16s. There are plenty of mid-lengths going high round counts and doing it with ease. Its not a new thing anymore, its been out, shot a lot, and proven reliable thus far by a lot of the "industry professionals". I really like Simon and I am sure he will come in here and make me feel stupid but I prefer mid-length guns and I'm happy with them.

[JAD]

Sorry, that needed rephrasing.

I don't know nothing and I'm sure you all are very knowledgeable. Searching on 'midlength ' is pretty illuminating.

[John Hearne]

The alternative view is that the carbine gas system, even at 14.5" is over-gassed for optimal performance.

For instance, if the carbine length gas system wasn't overgassed, there would be no need for all of the sundry extractor upgrades that have been offered over the years. If you take bolt carrier groups setup for rifle gas systems, a significant percent will puke in a carbine gas system, even 14.5". If you swap the extractor spring and insert to a carbine one, it runs fine. This appears to be a result of the increased bolt carrier velocity associated with the carbine gas system. You have to hold on to the case more strongly because the action is cycling more vigorously.

Similarly, there is a reason that we need to be careful with buffer weights and actively design to avoid bolt bounce (especially in full auto). The action is cycling so violently that the bolt carrier group hits so hard that it bounces backwards. It only hits that hard going forward because it went back that fast. How do we fix this? By adding weight to slow the action or by using multiple weights inside the buffer to create a "Three Stooges" effect of one smacking into the next.

Along the same line, why do we worry about magazine design more with carbine gas systems? Because the action is cycling faster and it is important that the magazine feed the next round up quickly enough to avoid interruption of the firing cycle. This is a timing issue. It arises because we are cycling the bolt carrier group faster and therefore the magazine needs to feed faster.

There seems to be a gold standard for AR reliability - the rifle length gas system. I'm no engineer but strongly suspect that if you measured the bolt carrier group velocity in the various systems, you would find that the rifle length gas system moves the slowest. Every other combination of barrel, port size, gas tube length, is going to be faster. The closer (aka slower) the times are to the rifle standard, the more reliable the gun will be.

Remember there are multiple considerations for optimal. Two are immediate reliability and long term durability. I suspect that the over-gassed carbine system very deliberately trades immediate reliability for long term durability. I suspect and the circumstantial evidence suggests that the mid-length gas system offer similar levels of immediate reliability but offer increased long term durability.

[Malamute]

^^^ This is about my take on it.

I understand and agree that the carbine system has had the most research and testing done on it, but its because it needed the research and testing to get to the point it is at, and is still not quite in the same level as the rifle length guns for overall reliability and longevity, from my understanding. If one wants shorter guns, carbine is the way to go. They work, and work well. If 16" is OK, I like the mid, with no scientific basis, other than I like the way they look and it makes sense that the lower port pressure will be less violent on the parts. My true love in ARs is rifles though. If I could have only one, that would be my first choice. Everything is a compromise in some way. Rifles do what I want and cause less heartburn to me (muzzle blast being a large point for me). No concern over which buffer, spring, port size, ammo, magazines, extractor springs. I also greatly dislike the movement on carbine stocks when shooting with a scope. Just my own peeve.

I'm not concerned if my personal like is "the best!", just that they work well. They all seem to. Some with less fanfare than others, but they all work.

My limited experience with mainly Colt SP1 rifles, and one H-bar is that Ive had more malfunctions with AK type guns than AR's. My opinion is not based on extensive experience, and is worth about what you paid for it.

[EMC]

Who knows the story of Mark Westrom (former US Army ordinance officer) at Armalite and how they came to use the mid-length system? I have been searching for documentation, but most of it is simple FAQ type stuff in the armalite page.

[BWT]

The alternative view is that the carbine gas system, even at 14.5" is over-gassed for optimal performance.

For instance, if the carbine length gas system wasn't overgassed, there would be no need for all of the sundry extractor upgrades that have been offered over the years. If you take bolt carrier groups setup for rifle gas systems, a significant percent will puke in a carbine gas system, even 14.5". If you swap the extractor spring and insert to a carbine one, it runs fine. This appears to be a result of the increased bolt carrier velocity associated with the carbine gas system. You have to hold on to the case more strongly because the action is cycling more vigorously.

Similarly, there is a reason that we need to be careful with buffer weights and actively design to avoid bolt bounce (especially in full auto). The action is cycling so violently that the bolt carrier group hits so hard that it bounces backwards. It only hits that hard going forward because it went back that fast. How do we fix this? By adding weight to slow the action or by using multiple weights inside the buffer to create a "Three Stooges" effect of one smacking into the next.

Along the same line, why do we worry about magazine design more with carbine gas systems? Because the action is cycling faster and it is important that the magazine feed the next round up quickly enough to avoid interruption of the firing cycle. This is a timing issue. It arises because we are cycling the bolt carrier group faster and therefore the magazine needs to feed faster.

There seems to be a gold standard for AR reliability - the rifle length gas system. I'm no engineer but strongly suspect that if you measured the bolt carrier group velocity in the various systems, you would find that the rifle length gas system moves the slowest. Every other combination of barrel, port size, gas tube length, is going to be faster. The closer (aka slower) the times are to the rifle standard, the more reliable the gun will be.

Remember there are multiple considerations for optimal. Two are immediate reliability and long term durability. I suspect that the over-gassed carbine system very deliberately trades immediate reliability for long term durability. I suspect and the circumstantial evidence suggests that the mid-length gas system offer similar levels of immediate reliability but offer increased long term durability.

This is all good info. I've "known" this stuff but didn't think to apply this in this discussion. Makes perfect sense 5-coil springs, black inserts, anti tilt followers, etc.

Carbine gas systems do run at higher pressures. I wonder if there's a percentile necessary of barrel to gas tube length to gas port ratio that keeps things optimized.

Fascinating stuff.

God Bless,

Brandon

ETA: I said I know stuff as a tongue in cheek to say even though I'm familiar with those things but didn't stop to consider it. Thanks for sharing John.

[GJM]

What I think SLG said, was that the 14.5 Colt, with a carbine gas system, is the most proven combination out there, by virtue of how many have been made for the military.

[El Cid]

I wanna hang out with Rob. He's either pretty cool or a douche bag and I don't think we will ever know until there is real life interaction.

I've met him. I've shot with him in classes and competition. I've drank beer and broken bread with him and I consider him a friend. He's actually a cool dude and a very good shot. Yea his internet style is a little rough around the edges... But he just wants data to show why something is better or worse. It's an engineer thing. Lol!

[John Hearne]

In the interests of full disclosure, I'm not trying to be an asshole, it just comes naturally.

[Malamute]

In other threads that completely duplicate this one in content, SLG mentioned several issues with midlengths and expressed concern that they were unproven. Ain't none of you said anything that makes me think you know a lot more than SLG about high round count ARs.

I sort of recall that, but not the details. Do you have a link? I searched but didnt find it.

I'm open to learning more, good or bad as relates to my choices.

[JAD]

I sort of recall that, but not the details. Do you have a link? I searched but didnt find it.

I'm open to learning more, good or bad as relates to my choices.

There's stuff scattered throughout several threads -- as I said this is a retread thread, and I'm not surprised no SMEs are participating in it. Some of the most direct comments are in this thread:
https://pistol-forum.com/showthread.php?17164-HK-carbine/page4
Particularly post 144.

The arguments against midlength seem to be very similar to those against the springer xd: they at least used to break a lot, and no major agency has gotten one through testing. That, and working hard on an 'advancement' that makes your .22 rifle recoil less makes you look like a little girl.

[orionz06]

The arguments against midlength seem to be very similar to those against the springer xd: they at least used to break a lot, and no major agency has gotten one through testing. That, and working hard on an 'advancement' that makes your .22 rifle recoil less makes you look like a little girl.

Who has broken a mid length AR? Who has tested one that wasn't a carbine length barrel, ie, not properly gassed? Short of the 14.5" middies I've not heard of one breaking, short of homebrew DelTon kit guns.

[Malamute]

There's stuff scattered throughout several threads -- as I said this is a retread thread, and I'm not surprised no SMEs are participating in it. Some of the most direct comments are in this thread:
https://pistol-forum.com/showthread.php?17164-HK-carbine/page4
Particularly post 144.

The arguments against midlength seem to be very similar to those against the springer xd: they at least used to break a lot, and no major agency has gotten one through testing. That, and working hard on an 'advancement' that makes your .22 rifle recoil less makes you look like a little girl.

OK, I recall it now. Thanks for the link. Good points. Will read it in detail.

[breakingtime91]

JAD, you profile picture shows you shooting a weaver stance. Not sure I would take your advice on what makes someone more efficient. The term about "looking like a little girl" proves what? I hate statements like this, they have no meaning or place in a constructive dialogue.

[jeep45238]

Carbine gas systems do run at higher pressures. I wonder if there's a percentile necessary of barrel to gas tube length to gas port ratio that keeps things optimized.



Just food for thought, but a rifle (11 gas, 20 barrel) is 55%, a middy 16 (9 gas, 16 barrel) is 56.25%, and a carbine 14.5 (7 gas, 14.5 barrel) is 45.5%. It seems that there's about a 10% margin of error for gas port placement to make things work (45-55% gas tube/barrel length) for standard systems. Some companies offer an intermediate length, but not standardization on that or the barrel length (noveske - 9.5 gas, 18 barrel is 52%). The percentages are a rough indicator for host much "work" the action gets, with higher % having less input to the carrier; like some things in life more isn't always better but you need enought o make things work. On the inverse, running less than I think where people get in trouble is putting a middy on a 14.5 system (9 gas, 14.5 barrel, 5.5 inches post port = 62.06%). The further from an original design you get, the more tuning you need. Look at 5" .45ACP 1911's versus those little 3" buggers and the tricks employed, with how fidgity they can be when not perfectly cleaned and lubed.

There's some boutique stuff like Noveske, which offer rifle, middy, carbine, and their own length (intermediate, 9.5") on various length barrels, but I'd imagine that running anything but full strength 5.56 NATO through them would cause things to choke if they're too far outside the standard parameters. But typically I don't think people run .223 Tula through their KAC or Noveske setups.

[breakingtime91]

I think he was summarizing, or stating the takeaway, from some people in that other thread. I'm not sure and I'm not about to read that thread again to figure out if I'm right or wrong. Because: lazy. :p

See; my sense of humor just sucks this weekend, sorry Tom

[StraitR]

See; my sense of humor just sucks this weekend, sorry Tom

BT, your internet style is a little rough around the edges. ;)

[BWT]

Just food for thought, but a rifle (11 gas, 20 barrel) is 55%, a middy 16 (9 gas, 16 barrel) is 56.25%, and a carbine 14.5 (7 gas, 14.5 barrel) is 45.5%. It seems that there's about a 10% margin of error for gas port placement to make things work (45-55% gas tube/barrel length) for standard systems. Some companies offer an intermediate length, but not standardization on that or the barrel length (noveske - 9.5 gas, 18 barrel is 52%). The percentages are a rough indicator for host much "work" the action gets, with higher % having less input to the carrier; like some things in life more isn't always better but you need enought o make things work. On the inverse, running less than I think where people get in trouble is putting a middy on a 14.5 system (9 gas, 14.5 barrel, 5.5 inches post port = 62.06%). The further from an original design you get, the more tuning you need. Look at 5" .45ACP 1911's versus those little 3" buggers and the tricks employed, with how fidgity they can be when not perfectly cleaned and lubed.

There's some boutique stuff like Noveske, which offer rifle, middy, carbine, and their own length (intermediate, 9.5") on various length barrels, but I'd imagine that running anything but full strength 5.56 NATO through them would cause things to choke if they're too far outside the standard parameters. But typically I don't think people run .223 Tula through their KAC or Noveske setups.

You'd be surprised.

https://www.ar15.com/archive/topic.html?b=2&f=381&t=247067

I'd think not either but I've used it for years. Candidly, if it keeps guys shooting and it's cheap why not?

I realized most of the carbine matches I was shooting years ago were 30-50 yards and in. Reduced size targets were used but at those distances as long as you can run steel cased ammo reliably you're not going to notice if it's 3-4 MOA ammo.

Then there's the whole "It should be able to run anything at that price".

Interesting to reflect on the measurements of gas lengths to barrel lengths. I believe you're correct, but keeping that in mind considering how much modification had to be introduced for the Carbine length and short barrel AR's that might have to do with that 45% gas length to barrel length versus 55%. In regards to 5 coil springs over 3, inserts under the extractor, H-Buffers, M4 Feed ramps, better magazines, etc.

Fascinating stuff for sure.

God Bless,

Brandon

[BWT]

Not to beat a dead horse but in case this topic does get revisited.

Here's some sound insights on the Midlength and Carbine Length gas systems by Mike Pannone on another forum.

http://www.m4carbine.net/showthread.php?97540-Mid-Length-Gas-Systems-and-the-M4

I read it a few days ago and thought it was worthwhile enough to post it here for longevity.

God Bless,

Brandon

[mmc45414]

Just food for thought, but a rifle (11 gas, 20 barrel) is 55%, a middy 16 (9 gas, 16 barrel) is 56.25%, and a carbine 14.5 (7 gas, 14.5 barrel) is 45.5%. It seems that there's about a 10% margin of error for gas port placement to make things work (45-55% gas tube/barrel length) for standard systems. Some companies offer an intermediate length, but not standardization on that or the barrel length (noveske - 9.5 gas, 18 barrel is 52%). The percentages are a rough indicator for host much "work" the action gets, with higher % having less input to the carrier; like some things in life more isn't always better but you need enought o make things work. On the inverse, running less than I think where people get in trouble is putting a middy on a 14.5 system (9 gas, 14.5 barrel, 5.5 inches post port = 62.06%). The further from an original design you get, the more tuning you need.

I thought this was interesting, and I laid this out:
9255
to consider the percentage of deviation from the rife, if that is the base line. I was kinda surprised to realize the CAR system is 20% more compact than the rifle. If that leads to it being abrupt, then I can understand it being abrupt. If that leads to it functioning reliably, then I would expect it damn sure would. The thread over on M4 inferred what I was thinking, that probably much of the harshness is attributed to the 16" CAR, since it is even 8% more aggressive as compared to the M4.

Of course I came across this thread right after I splurged on a nice BCM barrel, a 16" middy... It does shoot smoothly! :)

[Unobtanium]

About that dwell-time...

https://www.youtube.com/watch?v=cmZSFBy9CZ8

[BWT]

About that dwell-time...

https://www.youtube.com/watch?v=cmZSFBy9CZ8

Yeah, but how many coils was his extractor spring?

:)

All joking aside, and I didn't mean to stir up the same controversy but Mike's commentary does lend credibility to the notion that there is an appropriate gas associated with a barrel length based on usage.

He indicated that the 7.5'' Carbine gas on a 14.5'' was overgassed but that he indicated it was effective for the usage as intended.


The addition of 1.5" from the military configuration (14.5"bbl>7.5"tube) over-gassed an already over-gassed design.

But he goes on to say
The 14.5 over gassing was by design for reliability under adverse combat conditions. then ends the post with
I like and run both and for shootability I favor the middy. In the end they both work fine so pick what yolu like..

Quotations from post #2 located http://www.m4carbine.net/showthread.php?97540-Mid-Length-Gas-Systems-and-the-M4 here.

I really think at the end of the day that's really what it boils down to. Both will work, both are reliable, and both were designed with two different functions in mind. In the end, it's preference.

I think that's how I'm going to resolve this dilemma and treat this subject.

God Bless,

Brandon

[frozentundra]

So does anybody know what the spec is on the gas port size on a Colt M4 vs a 6920 and 6720?

I did a quick google search and saw the number .063 quoted often regarding the M4, but I didn't see any actual reference material cited. Likewise for the 6920; there were people saying .063 as well, but no links to supporting information. The gas port diameter must be just as important as the location, correct?

That link to Mike Pannone above was interesting. From post #8 in that thread:
"The key for buffer and spring weight suitability is the rifle when held loosly in your hands and 1 round chambered, empty mag in the well should lock to the rear. Also with a full magazine +1 in chamber the rifle should cycle reliably. The full mag +1 is to validate that the extra friction exerted by the top round of the full mag does not push you in the wrong direction on the reliability scale."

Just for shits and giggles I'm gonna try this with my BCM middy with several different loads, including cheap steel cased wolf, just to see what happens. This particular gun has cycled several hundred rounds of steel cased wolf in extreme cold weather(I think down about -20 once) with no malfunctions or failures to lock back when empty.

[JAD]

JAD, you profile picture shows you shooting a weaver stance. Not sure I would take your advice on what makes someone more efficient. The term about "looking like a little girl" proves what? I hate statements like this, they have no meaning or place in a constructive dialogue.

My profile picture is from 1997, when I was better looking, which isn't saying much. All of my statements were an attempt to paraphrase what SLG said in the thread which I first referenced and then linked. I don't have the standing to agree or disagree with him; the point of my posts in this thread have been to remind us that we have talked about this before, and to remind us of what an SME said the last time any of them participated in one of these threads.

And your profile picture shows you being a dog. I don't know what standing a dog has to comment on mid length gas systems, they can't even manage a beer can grip.

[rob_s]

If you can't understand that gas at 32,900psi will erode the orifice it is flowing through sooner than gas at 26,500psi, I'm not sure that ANYTHING is going to help you see any merits. More succinctly, I think you choose not to see any merits, much like I know a few people who think their M14 can do anything your M4 can do, except with 1500# more energy.

So, after all of this, still nothing?

Where is the testing that shows one barrel failing before the other?

[Unobtanium]

So, after all of this, still nothing?

Where is the testing that shows one barrel failing before the other?

I believe gas tubes to be the weak link when heavier (M4A1), or tapered barrels are used, and the mildength gas tube is not nearly the weak link the carbine gas tube is. Joel of V7 has done numerous tests, and I would contact him for further data, so I don't muddle anything in translation.

[Unobtanium]

Yeah, but how many coils was his extractor spring?
Who cares? It ejected to 4 o'clock. It has passed the Internet's test of proper function. Done and done!
:)

All joking aside, and I didn't mean to stir up the same controversy but Mike's commentary does lend credibility to the notion that there is an appropriate gas associated with a barrel length based on usage.

He indicated that the 7.5'' Carbine gas on a 14.5'' was overgassed but that he indicated it was effective for the usage as intended.



But he goes on to say then ends the post with .

Quotations from post #2 located http://www.m4carbine.net/showthread.php?97540-Mid-Length-Gas-Systems-and-the-M4 here.

I really think at the end of the day that's really what it boils down to. Both will work, both are reliable, and both were designed with two different functions in mind. In the end, it's preference.

I think that's how I'm going to resolve this dilemma and treat this subject.

God Bless,

Brandon

Function is function. There is nothing magical about it. It is a mixture of pressure, volume, and time. That is all. That is it. If you have less pressure, you need more volume. If you have less time, and less pressure, you need MORE volume. If you have more time and more pressure, you need less volume, and so on. This is how the 2" barrel, and the 16" barrel, and the 20" barrel, all function adequately. If you take the time to properly mix/match all of the variables, you WILL GET function. All of this nonsense about "ideal lengths" and whatnot is just that. You can manipulate the other variables to support the system quite happily. Debating it is simply some form of masturbatory time-kill. Which of course like it's namesake, can be enjoyable at times, mind you.

All this said, what is NOT debatable, is that the more pressure that flows through the gas port, the more each event damages said gas port (changes its dimension).

Another thing that cannot be neglected, is that bore diameter changes the significance of the gas port diameter. For example, some manufacturers use a tapered bore. This will increase pressure (one of our variables), without altering time or volume, thus the port must be closed (volume altered) to maintain identical function to a barrel without a tapered bore.

Thus when you pin-gauge a BCM barrel, and then a DD barrel, and then say, a Centurion barrel, you may get very different gas-port diameters, and yet they all like the same buffer. Or the ports may be identical, yet one barely runs an H, while the other can chug along with an H3.

This is also why many manufactures "go big" on the ports. So that they do not have to test each lot of barrels to see what the bore is. I remember Spikes Tactical doing similar testing on their 300BLK Compressor. The bore diameter varied by 0.001" from one lot to another, and to achieve identical BCG function, gas port size was modified almost 10 thou! That is how variable gas port size is, based on ONLY ONE other variable (pressure).

So if we are to jerk ourselves raw over port to muzzle to chamber distances, let us also include bore diameters, etc. etc. so that the endless debate may become more meaningful. Otherwise, we are arguing about valve-train components without ever considering what heads they are to fit.

Ultimately, I feel that chamber to port to muzzle distances don't mean a darn thing, except as regards port erosion, so long as the SYSTEM as a whole is taken account of.

[BWT]

Who cares? It ejected to 4 o'clock. It has passed the Internet's test of proper function. Done and done!

I was joking. Either my sarcasm doesn't come through text or I'm not funny. I'm really banking on the first one. I figured it'd be a ludicrous situation given the barrel length is... what 7 times shorter than a 14.5? I have no idea how long that gas tube is.


All this said, what is NOT debatable, is that the more pressure that flows through the gas port, the more each event damages said gas port (changes its dimension).

Agreed.

God Bless,

Brandon

[breakingtime91]

My profile picture is from 1997, when I was better looking, which isn't saying much. All of my statements were an attempt to paraphrase what SLG said in the thread which I first referenced and then linked. I don't have the standing to agree or disagree with him; the point of my posts in this thread have been to remind us that we have talked about this before, and to remind us of what an SME said the last time any of them participated in one of these threads.

And your profile picture shows you being a dog. I don't know what standing a dog has to comment on mid length gas systems, they can't even manage a beer can grip.

well played. Truthfully my dog could probably take me, even if I was armed with a AR15 that had a carbine length gas system...

[GJM]

well played. Truthfully my dog could probably take me, even if I was armed with a AR15 that had a carbine length gas system...

If you are going to wrestle with a bear or large dog, I hear it is good planning to remove any front sight, as it hurts less going in there.

[Unobtanium]

I was joking. Either my sarcasm doesn't come through text or I'm not funny. I'm really banking on the first one. I figured it'd be a ludicrous situation given the barrel length is... what 7 times shorter than a 14.5? I have no idea how long that gas tube is.



Agreed.

God Bless,

Brandon

I think it was my dry humor thay didn't translate... ;)

[Malamute]

I re-read that older thread that was linked. I re-read some of the newer stuff. I agree that the standard carbine system is the standard. Mid length sounds like a good idea and makes sense, but the bottom line is that they don't have the track record of use the carbine system does. Until it does, (which may be never to be realistic) its a matter of believing its good, and we have smaller numbers of examples with higher round counts for proof of concept of any perceived or theoretical advantages. If one is OK with that level of confidence, great. The mid just doesn't have the track record of use that carbine gas guns do.

Apparently some people had problems with mids, perhaps more so in the past. I dont know what those problems were, or if the guns were changed since then to correct the shortcomings, but the bottom line is that we just don't have the level of firsthand experience telling us the mids are as reliable and functional as the good examples (Colts) of carbines, despite the theory that they should be slightly less hard on parts. Theory, so far. Only time will tell, and as I said before, we may never get to the same level of use seen by the carbines. I entirely see the point of those that have said theres not really enough good reason to switch to mid, as the carbines do all they are asked to, and not operating on theory to do so. The mid users are basically the beta testers until theres more time and use on good examples of them, even then, one gets to choose to be in the beta test group rather than sticking with known quantities as far as reliability and performance. If life and limb are dependent on a thoroughly reliable arm, then we know which one that is.

I still like rifles, but its not a rifle friendly world in many ways.

I used to tell my girlfriend I was slow, but trainable.

[orionz06]

14.5" carbine length guns have that track record...

[Unobtanium]

14.5" carbine length guns have that track record...

Improvement happens, though.

[mmc45414]

I agree that the standard carbine system is the standard. Mid length sounds like a good idea and makes sense... its a matter of believing its good, and we have smaller numbers of examples with higher round counts for proof of concept of any perceived or theoretical advantages. If one is OK with that level of confidence, great. The mid just doesn't have the track record of use that carbine gas guns do.... Theory, so far. Only time will tell, and as I said before, we may never get to the same level of use seen by the carbines. I entirely see the point of those that have said theres not really enough good reason to switch to mid, as the carbines do all they are asked to, and not operating on theory to do so. The mid users are basically the beta testers... I still like rifles, but its not a rifle friendly world in many ways.

Yes, great post, though I would contend that we may have moved a bit beyond beta, but there is no definition. I originally went with the carbine length for all of those proven reasons. In the intervening ~decade the mid has become "more" proven, proven enough for me to go that way in the process of upgrading. I will admit, the Filthy 14 experiment made me more comfortable, and was part of the reason I went the way I did, including BCM.

And yeah, spending more time behind my 26" rifle length gas gun that doesn't move the prairie dog mound out of the field of view also gave me more of a desire to mimic that recoil impulse, and though I did not hook one up to the Hewlett-Packard model 5710a with flame analyzing detectors, nearly duplicating the gas/barrel ratio of the rifle seems like not a huge departure.

[orionz06]

Improvement happens, though.

In the way of 16" carbine length guns?


Sent from my Nokia 3310 using an owl

[Unobtanium]

In the way of 16" carbine length guns?


Sent from my Nokia 3310 using an owl

I rather like a 14.5 middy. 14.5, regardless, and mid-gas is just a step up in durability and longevity.

[Wondering Beard]

I rather like a 14.5 middy. 14.5, regardless, and mid-gas is just a step up in durability and longevity.

Wait, I thought the 16" was preferred for a middy and the 14.5" middy was really dependent on ammunition?

[Unobtanium]

Wait, I thought the 16" was preferred for a middy and the 14.5" middy was really dependent on ammunition?

My noveske 14.5 middy fed anything and ran fine, and I've heard nothing but good about the 14.5 middies currently being tested.

[Sadmin]

My noveske 14.5 middy fed anything and ran fine, and I've heard nothing but good about the 14.5 middies currently being tested.
How many rounds do you have on that noveske? Asking because my 14.5 BCM mid didn't start to show problems until north of 4k...

Sent from my SAMSUNG-SM-G930A using Tapatalk

[MistWolf]

I re-read that older thread that was linked. I re-read some of the newer stuff. I agree that the standard carbine system is the standard. Mid length sounds like a good idea and makes sense, but the bottom line is that they don't have the track record of use the carbine system does

The 16 inch barreled carbine gassed AR also does not have the track record of the 14.5 inch carbine gassed AR

[Malamute]

^^^ Good point, though they've been on the commercial market since the 70s I believe.

I'm not by any means saying I don't like the mids, but I agree with a number of posters that they simply don't have the real life track record and R&D behind them. I like the mid, but I'm not a door kicker or person whose life depends on it.

Being starkly realistic about any possible defensive use of a long gun, I'm far more likely to have a lever action at hand than an AR, simply because of my location and lifestyle.

[John Hearne]

Asking because my 14.5 BCM mid didn't start to show problems until north of 4k...

What issues did you have? I'm asking because I've been buying BCM 14.5" middies for work. I have five and number six is on the way. We haven't had any issues but they're under 500 rounds at this time and we're running full-power ammo.

[Unobtanium]

How many rounds do you have on that noveske? Asking because my 14.5 BCM mid didn't start to show problems until north of 4k...

Sent from my SAMSUNG-SM-G930A using Tapatalk

4 to 5k. What issues did your bcm have?

[Sadmin]

FTFs... anything from PMC to IMI m193. I wrote BCM at the time of the issues and they had me send the upper in. This was back when they pinned the GB but they noted significant leakage around it.

[Unobtanium]

FTFs... anything from PMC to IMI m193. I wrote BCM at the time of the issues and they had me send the upper in. This was back when they pinned the GB but they noted significant leakage around it.

Was it returned to you, fixed? This does not sound like a middy problem. More like a qa/qc problem.

[Sadmin]

Yes... in part. I could no longer utilize H2 buffers. No biggy, and you are probably correct. Just flinched me enough to stick with 16" middys because: gun forum induced fear. I dont go around advocating against 14.5s or anything - I was just interested in the Noveske history.

[Maple Syrup Actual]

It's probably dumb for me to even enter into this thread as i lack the information to really explain the WHY of anything that follows.

But one thing I can say about mid-length gas systems: I do deal with Colt Canada who do an absolutely absurd degree of testing on every aspect of their guns. For example, they use a specific texture on their specific polymer stocks to prevent beard freezing below a specific temperature, as identified through (presumably unpleasant) experimentation. And their C8 carbine has a 15.7" barrel because testing in 0.1" increments identified an accuracy node with NATO ammo at that length. The fact that increasing it to 16" would allow them to potentially investigate selling to the largest AR market on the planet means nothing to them. There is an absolute lack of interest in doing anything for marketing, or even sales, purposes at Colt Canada.

Anyway...they do not use a standard gas system. I don't know the dimensions on my IUR offhand, but it's not a normal carbine system. And Colt Canada absolutely adhere to the "no deviation without performance gains" ethos.

[GJM]

It's probably dumb for me to even enter into this thread as i lack the information to really explain the WHY of anything that follows.

But one thing I can say about mid-length gas systems: I do deal with Colt Canada who do an absolutely absurd degree of testing on every aspect of their guns. For example, they use a specific texture on their specific polymer stocks to prevent beard freezing below a specific temperature, as identified through (presumably unpleasant) experimentation. And their C8 carbine has a 15.7" barrel because testing in 0.1" increments identified an accuracy node with NATO ammo at that length. The fact that increasing it to 16" would allow them to potentially investigate selling to the largest AR market on the planet means nothing to them. There is an absolute lack of interest in doing anything for marketing, or even sales, purposes at Colt Canada.

Anyway...they do not use a standard gas system. I don't know the dimensions on my IUR offhand, but it's not a normal carbine system. And Colt Canada absolutely adhere to the "no deviation without performance gains" ethos.


http://www.coltcanada.com/c8-carbines.html


Per their website, the C8 has a "special carbine chamber and gas system."

[Malamute]

http://www.coltcanada.com/c8-carbines.html


Per their website, the C8 has a "special carbine chamber and gas system."

Just was looking at that myself. If its different than the standard, it isn't as long as a mid, for whatever reason/however they changed it.

Barrel is interesting. Looks like a sleeve over the barrel with a stop for a bayonet. Sort of the opposite of m4 grenade launcher cuts.

[Maple Syrup Actual]

Yeah. The gas tube is, iirc, not only an oddball length, closer to carbine than mid, but it's also straight.

Sent from my SM-N900W8 using Tapatalk

[Malamute]

Yeah. The gas tube is, iirc, not only an oddball length, closer to carbine than mid, but it's also straight.

Sent from my SM-N900W8 using Tapatalk

We don't make any judgements on gas tube orientation around here, or which restroom it uses. :)

[Maple Syrup Actual]

Well, if people here can be that welcoming, then I guess I'll admit that I believe that the dimensions are such that it could go both ways.

Sent from my SM-N900W8 using Tapatalk

[Unobtanium]

Yes... in part. I could no longer utilize H2 buffers. No biggy, and you are probably correct. Just flinched me enough to stick with 16" middys because: gun forum induced fear. I dont go around advocating against 14.5s or anything - I was just interested in the Noveske history.

My theory has always been:

Take pmc bronze .223
Take a clean weapon.
Gunsscubber the bcg off.
Load a full 30 round mag, 1 in the chamber. 31 on board. Fire 2 rounds, reload and repeat. Do this x10.
Take a mag with 2 rounds. Chamber one. Fire twice and verify lockback. Do this 10 times.

For both of these tests, the weapon should be held as loosely as safely and intelligently possible, allowed to recoil freely and not against a shoulder or other impediment.

Pick the heaviest buffer and spring combo this works for, all 20 iterations.

You should have a weapon setup that is dead nuts reliable with any brass cased ammo that is in spec.

[Whiskey_Bravo]

Anyone here have any experience with different muzzle devices on the 14.5" carbine system? Trying to decide if something like a Warcomp or BCM Gunfighter would offer any substantial advantage over an A2.

Sorry for the slight thread drift.

[Appalachained]

Anyone here have any experience with different muzzle devices on the 14.5" carbine system? Trying to decide if something like a Warcomp or BCM Gunfighter would offer any substantial advantage over an A2.

Sorry for the slight thread drift.

I have the BCM Mod1 1.5" on a 6921. It's the only one I've had on it. It's no louder than an A2 and jumps a little less. It feels about the same as the Battlecomp on my Noveske 16".

[texasaggie2005]

Anyone here have any experience with different muzzle devices on the 14.5" carbine system? Trying to decide if something like a Warcomp or BCM Gunfighter would offer any substantial advantage over an A2.

Sorry for the slight thread drift.
Currently have an original Warcomp on a 14.5" Colt. I prefer it, over the A2 on my 16” Colt.

[Rick62]

I have a mod. 1 on a 14.5 middy, so obv not an apples to apples comparison. For what its worth, the mod 1 does seem less offensive than some other, more aggressive designs. I don't note any negative effects behind the gun, and I don't hear any complaints from other shooters on the line.
Possibly of interest to you, given your intended use on a 14.5 carbine, is a discussion on the design of the comp and how it affects gas pressure. More discussion at the link, but the design of the mod 1 basically adds back pressure via an expansion chamber.

http://www.m4carbine.net/showthread.php?135121-New-BCM-rail&p=1889504#post1889504

[Whiskey_Bravo]

I am a big fan of the BCM comp. I had one on one of their 14.5" Missy's previously and most recently on a 16" middy. Both uppers have since been sold to find a new Colt upper project.

I plan on building a Non-NFA (Pinned and Welded) around a 14.5" Colt SOCOM barrel. Was having difficulty deciding upon what muzzle device to use. I am a big fan of the BCM device, but I see some Surefire suppressors in my future, so I am pretty much set on one of the new birdcage style warcomps.

[Malamute]

I have an unfired BCM mod 0 compensator (http://www.bravocompanyusa.com/BCMGUNFIGHTER-Compensator-s/165.htm)from a new barrel if anyones interested. Id make a good deal on it

[rob_s]

I rather like a 14.5 middy. 14.5, regardless, and mid-gas is just a step up in durability and longevity.

Regardless of the fact that you he's no way to measure or prove said durability or longevity.

Ok Linus.

9859

[Unobtanium]

Regardless of the fact that you he's no way to measure or prove said durability or longevity.

Ok Linus.

9859

I cannot prove that dropping 200# on your foot would hurt more than dropping 20# on your foot, but if one were destined to happen, I'd wager you would prefer the 20#. The force exerted on the bolt, while not as much disparity, is a similar argument.

[Default.mp3]

Last week’s NDIA Armaments Forum ended with a briefing by Naval Surface Warfare Center – Crane, of what is this year’s most applicable topic, for both the US military as well as manufacturers of commercial AR variants. Last year Crane unveiled their findings regarding KeyMod vs M-Lok. This year it’s the performance of a mid-gas system on an M4 carbine.

http://soldiersystems.net/blog1/wp-content/uploads/2018/05/img_9705.jpg


NSWC-Crane, or Crane as it is commonly known, is located in rural Indiana. In addition to providing a wide range of acquisition services for the US Navy, they are also responsible for the test, evaluation, procurement and life-cycle management of SOF weapons. It’s in this role that they evaluated the mid-length gas system for United States Army Special Operations Command M4A1 carbines.

Gas System History

The M16 Rifle and variants use a 20” barrel and gas system. This rifle length gas system uses a gas tube 15” in length with gas port at 13”. The well distance is approximately 7”.

http://soldiersystems.net/blog1/wp-content/uploads/2018/05/D3B46C40-B7BE-452B-88FE-BAA8D70BC108-440x288.png

When the M4 was developed, research concluded the Army should utilize a 14.5” barrel for the M4 & M4A1 carbines

This necessitated redesign of the M16 gas system because a 14.5” barrel with a rifle length gas system had only 1.3” dwell distance. Consequently, they gas port was moved to 7.8” from bolt face on M4 offering 6.7” dwell distance.

This decrease in distance from the bolt face to the gas port resulted in an increased port pressure in the M4 carbine when compared to M16 rifle. The port pressure of the M4 at 7.8” from the bolt face is 17,000 psi, while port pressure at 13” from bolt face of the M16 is 10,000 psi.

Mid-Gas Testing included:

– Endurance
– Reliability
– Precision
– Muzzle Velocity
– Terminal Velocity (@100 yards)
– Bolt Speed
– Low Temperature (-60F)
– High Temperature (160F)
– Barrel Erosion

However, the briefing did not address every area of testing.

Endurance & Reliability

So far, Crane has put 30,400 rounds of M855A1 through three M4A1s equipped with 14.5″ cold hammer forged barrels and a mid-gas system with a gas block approximately 9.8″ from the bolt face.

http://soldiersystems.net/blog1/wp-content/uploads/2018/05/img_9704.jpg

They stated SOF M4A1s normally start to see accuracy degradation at around 6,000 rounds. But during testing of the mid-gas system, they’d hit 12,600 and still hadn’t seen any changes.

They also have only broken one bolt so far in testing, although I don’t think they’re ready to attribute the improved bolt performance to the mid-gas system.

The Crane team will finish testing up with 34,000 rounds per upper. It’s not that they don’t think the barrels can’t take more, but rather that they had to use the same lot of M855A1 to satisfy the accuracy portions of testing.

USSOCOM Accuracy Testing & Protocol

With this mid-gas system they are getting 5 MOA groups while the standard is 7 MOA. One of the three uppers was shooting 1 MOA, except for the tenth round which was still within limits.

Interestingly, USSOCOM tests accuracy differently than most others. They fire 10 rounds suppressed and another 10 rounds unsuppressed. They measure the extremes of the spread of impacts, rather than their closest points. Then, they do it again two more times and average the results to determine accuracy.

Muzzle Velocity

These measurements are averaged and validate what we know about the use of suppressors increasing muzzle velocity.

http://soldiersystems.net/blog1/wp-content/uploads/2018/05/8838A4AE-96DD-471D-B8DC-94FC1CB4E333.jpeg

Terminal Velocity

The velocity at 100 yards for mid-length weapons is 32.6 fps or 1.2%, higher for suppressed fire and 41.7 fps or 1.6%, higher for unsuppressed fire.

http://soldiersystems.net/blog1/wp-content/uploads/2018/05/1908FB5E-37F7-4D76-824A-FCAD774CCF16.jpeg

Cyclic Rate

Mid-length cyclic rate of automatic fire was 62.7 rounds per minute (rpm), or 7%, lower than carbine-length for suppressed fire and 127.2 rpm, or 16%, lower for unsuppressed fire.

http://soldiersystems.net/blog1/wp-content/uploads/2018/05/421F85CB-815F-4FB9-94DF-C00EBA744360.jpeg

Temperature High & Low

960 rounds were fired at 160F for Reliability at High Temp and another at -60F for Reliability at Low Temp.

For carbine-length weapons, 5 out of 65 malfunctions occurred during high temperature testing. For mid-length weapons, 1 out of 30 malfunctions occurred during high temperature testing. For high temperature testing, carbine-length weapons had 576.0 mean rounds between failures (MRBF) compared to 836.1 MRBF for ambient temperature testing and mid-length weapons had 2800 MRBF compared to 1993.8 MRBF for ambient temperature testing.

For carbine-length weapons, 27 out of 65 malfunctions occurred during low temperature testing. For mid-length weapons, 16 out of 30 malfunctions occurred during low temperature testing. For low temperature testing, carbine-length weapons had 333.3 mean rounds between failures (MRBF) compared to 836.1 MRBF for ambient temperature testing and mid-length weapons had 562.5 MRBF compared to 1993.8 MRBF for ambient temperature testing. Approximately half of the total malfunctions recorded for both carbine-length and mid-length weapons occurred during low temperature testing, so the relative rate of malfunctions between carbine-length and mid-length remained similar to that of ambient temperature testing.

Conclusion

Although testing to 34,000 rounds isn’t yet complete, the conclusion is simple. Use of a mid-gas system significantly extends the life of the overall weapon system. It also offers increased performance over a carbine-length gas system.

Implications

This information is particularly important for the US Air Force’s Improved Modular Rifle – Blue program which templates off of upper receiver group improvements adopted by USASOC (Brownells is offering a similar package for reference). While USASOC will upgrade up to 15,000 carbines, the AF wants to modify around 50,000 guns. That could be enough to force a major Technical Data Package update applicable to all services and creation of a GOTS upgrade for all M4s, regardless of service.

This government testing also validates what many commercial vendors have been offering for years.Source: http://soldiersystems.net/2018/05/14/nswc-crane-carbine-mid-length-gas-system-testing-shows-increased-performance/

Suck it, haters.

[orionz06]

Source: http://soldiersystems.net/2018/05/14/nswc-crane-carbine-mid-length-gas-system-testing-shows-increased-performance/

Suck it, haters.

Those are some rather substantial differences.


Regardless of the fact that you he's no way to measure or prove said durability or longevity.


I'd say that's at least enough to point things in the other direction, wouldn't you?

[rob_s]

Those are some rather substantial differences.



I'd say that's at least enough to point things in the other direction, wouldn't you?

About time all the zealots get some facts.

Doesn’t change the fact that everything up tomthat test was just a bunch of hysterical belief perpetuated by internet myth and “knowledge”.

Just because the facts end up supporting ones belief doesn’t mean their belief was previously based in fact. Or knowledge. Or experience. Or anything else valid.

[orionz06]

About time all the zealots get some facts.

Doesn’t change the fact that everything up tomthat test was just a bunch of hysterical belief perpetuated by internet myth and “knowledge”.

Just because the facts end up supporting ones belief doesn’t mean their belief was previously based in fact. Or knowledge. Or experience. Or anything else valid.


Not sour at all, I see... Your last four points though, those are ones that I suspect if you read around you'd see otherwise, should you so choose to take the blinders off.

[jeep45238]

About time all the zealots get some facts.

Doesn’t change the fact that everything up tomthat test was just a bunch of hysterical belief perpetuated by internet myth and “knowledge”.

Just because the facts end up supporting ones belief doesn’t mean their belief was previously based in fact. Or knowledge. Or experience. Or anything else valid.

https://yourlogicalfallacyis.com/

[OlongJohnson]

If anyone can find a downloadable version of the actual CRANE presentation document, that would be awesome. I did a quick google and didn't find it, although given the subject matter, that doesn't mean it's not readily available.

I am a fan of original sources.

[Casual Friday]

I've decided to nickname my 14.5" mid length "rob_s' spirit animal" in honor of this thread.

I forgot I had that upper until I reread this thread.

[StraitR]

Suck it, haters.

Ha! I love it. I guess reducing force, frequency, and heat to prolong the life cycle of a mechanical system wasn't such a novel idea after all. The reliability bit was icing. :)

Thanks for posting!

[orionz06]

Ha! I love it. I guess reducing force, frequency, and heat to prolong the life cycle of a mechanical system wasn't such a novel idea after all. The reliability bit was icing. :)

Thanks for posting!

And it's not like these aren't basic principles....

[StraitR]

And it's not like these aren't basic principles....


Exactly, but it takes the likes of Crane to publish a study for the luddites and curmudgeons to acknowledge them. Elementary critical thinking skills and 10 minutes spent with a middy is what it took for most.

[jeep45238]

Exactly, but it takes the likes of Crane to publish a study for the luddites and curmudgeons to acknowledge them. Elementary critical thinking skills and 10 minutes spent with a middy is what it took for most.

I wouldn't say that they have even aknowledged the results, based off their response.

[Default.mp3]

If anyone can find a downloadable version of the actual CRANE presentation document, that would be awesome. I did a quick google and didn't find it, although given the subject matter, that doesn't mean it's not readily available.

I am a fan of original sources.
https://partner-mco-archive.s3.amazonaws.com/client_files/1527866983.pdf

[Wondering Beard]

Source: http://soldiersystems.net/2018/05/14/nswc-crane-carbine-mid-length-gas-system-testing-shows-increased-performance/

Suck it, haters.

Question: I see that the test used M855A1 as ammo and a 14.5" barrel with a midlength gas system. Doesn't the use of essentially a +P round along with what I understand is an under gassed midlength system (16" is right but 14.5" makes it a bit under gassed for mid lengths, I was told, but I'm no expert) make the results less comparable than using a regular 5.56 pressure round and comparing a 14.5" carbine vs a 16" midlength? or would it make no difference?

[MistWolf]

Question: I see that the test used M855A1 as ammo and a 14.5" barrel with a midlength gas system. Doesn't the use of essentially a +P round along with what I understand is an under gassed midlength system (16" is right but 14.5" makes it a bit under gassed for mid lengths, I was told, but I'm no expert) make the results less comparable than using a regular 5.56 pressure round and comparing a 14.5" carbine vs a 16" midlength? or would it make no difference?

What primarily controls gas is the gas port diameter. The length from gas port to muzzle (Carbine, Middy, Rifle, etc.) determines how long there will be usable pressure at the gas port (which has nothing to do with how long the bullet is in the bore).

While the carbine length system takes longer to blow down, the middy taps into the barrel where gas pressure is lower. The higher the pressure, the tighter the tolerance of the port diameter must be to achieve the correct gas flow. It's about achieving a balance between blow down time and pressure at the gas port to provide good gas flow to the BCG.

[Unobtanium]

Question: I see that the test used M855A1 as ammo and a 14.5" barrel with a midlength gas system. Doesn't the use of essentially a +P round along with what I understand is an under gassed midlength system (16" is right but 14.5" makes it a bit under gassed for mid lengths, I was told, but I'm no expert) make the results less comparable than using a regular 5.56 pressure round and comparing a 14.5" carbine vs a 16" midlength? or would it make no difference?

M855a1 is not "+P". Its the same pressure as m855 currently as best as I can tell.

[jeep45238]

Isn’t a1 just a new bullet design?


Sent from my iPhone using Tapatalk

[Unobtanium]

Isn’t a1 just a new bullet design?


Sent from my iPhone using Tapatalk

Yes, but there are other new components as well, and the early lots used a very high pressure loading. They have been backing off on it for years, and it's currently hanging out around M855 spec, or a touch cooler.