Midlength Gas Systems (split from the Colt Midlength thread)

[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 and especially HERE 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.


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[JSGlock34]

Yup, and he sounds a lot like his Father HERE and especially HERE 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.


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