Thoughts on Piston Driven AR's

[WDW]

I was wanting input, preferably from someone who puts many, many thousands of rounds down range each year, on Piston Driven AR's. I am specifically looking at the Sig 516 if anyone has any experience with it. The fact that the gas key is integral to the BCG appeals to me, as that is a possible failure point on a DI gun (though not likely if loctited and properly staked). I have always run DI AR's but am wondering if there is any advantage.

[orionz06]

What is the disadvantage of a DI AR?

[WDW]

What is the disadvantage of a DI AR?
I don't know? That's why I'm asking. Are piston guns being made for no reason? I've never had a single problem with my DI AR, just curious.

[Jay Cunningham]

Piston ARs (specifically the HK416) were developed to meet a rather narrow operational requirement. Unfortunately, like so many other weapons and pieces of gear designed to meet a narrow operational requirement, a lot of average Joes look at them as the answer to their prayers simply because "if it's good enough for <insert favorite spec ops name here> its gotta be good enough for me!"

So here's the deal. If you find yourself in the following situation:


you tend to employ short barreled ARs
you tend to do a lot of your shooting suppressed
you find yourself shooting full-auto relatively frequently
you do not have reliable access to really good "mil-spec" ammo
you may have an op tempo which prevents you from a decent cleaning and lubrication regimen



A quality piston gun, such as a 10.5" HK416 may be right for you. Otherwise, there is probably no value added.

[WDW]

Piston ARs (specifically the HK416) were developed to meet a rather narrow operational requirement. Unfortunately, like so many other weapons and pieces of gear designed to meet a narrow operational requirement, a lot of average Joes look at them as the answer to their prayers simply because "if it's good enough for <insert favorite spec ops name here> its gotta be good enough for me!"

So here's the deal. If you find yourself in the following situation:


you tend to employ short barreled ARs-NO
you tend to do a lot of your shooting suppressed-NO
you find yourself shooting full-auto relatively frequently-NO
you do not have reliable access to really good "mil-spec" ammo-NO
you may have an op tempo which prevents you from a decent cleaning and lubrication regimen-NO

Well, I guess I'll forget that then. Thanks for the info. I had a feeling they were designed for suppression and SBR applications, both of which don't apply to me.

[Odin Bravo One]

Even though they may not be for you.............if one was so inclined as to purchase one because they wanted to dare to be different, there are really only two companies that have put their guns into hard use service and had them work reliably. Hk 416, and the LWRC M6. After that, most piston driven guns are junk. The others, Colt, Sig, etc have not been around long enough to establish if they have in fact cracked the code, or if they are just making money off the latest craze. Some are so bad that at carbine courses I actually make bets with the owners for how long before their gun has a show stopping malfunction that needs a parts replacement, or must disassemble to gun to clear the malfunction. Sad for them, I have not lost any of those bets yet. It's usually right around lunch time on the first day.

[Kyle Reese]

For the average end user, piston guns offer no real value added.

I'm not talking about DEVGRU / CAG guys running HK 416's in various operational roles, either.

On average, piston guns

-Are heavier

-Utilize far more proprietary parts necessary to keep them operational

-Are prone to suffer from carrier tilt unless the carrier is designed properly (and some are not)

Also, be aware that many of the so called "drop in" piston kits are a surefire way to make your reliable DI gun choke. There are timing issues, gas port pressure, buffer weight etc that all must sync in order to have a reliable weapon. Monkey around with those variables and get a "dammit, this piece of junk is jammin' again!!!" sort of response. :)

A well built DI gun is very reliable with lubrication, good mags and ammo. You can find brand new Colt SP6920's for sale for $1064, shipped to your FFL, from Palmetto State Armory (http://palmettostatearmory.com/2240.php). The 6920's are well made and will serve you well.

Other quality AR makers are BCM, Noveske, LMT, Daniel Defense and Knight's Armament Corporation.

I had the chance to shoot a 10.5" HK 416 at Blackwater and was very happy when I picked up my KAC SR15E3 and carried on. :)

[orionz06]

In reference to the Sig 516, just look at Sig's current crop of pistols that aren't what they used to be. If you did want a piston gun it would not be from them. Otherwise, I am not aware of anyone who has even posted anything about the 516 on any forums where I would trust the posters. I also have not been looking for info on it.


To add to what Jay said: When the piston conversion kits became popular (early 2000's IIRC) you did not have Daniel Defense, Noveske, BCM, and all the other companies that knew what they were doing when they made a gun. They did address many concerns in lesser quality guns, but came with their own sets of issues.

A little further discussion on the points Jay makes:

you tend to employ short barreled ARs: The companies mentioned make SBR's that work just fine.

you tend to do a lot of your shooting suppressed: If you understand what the suppressor does to the gun and make corrections they can work just fine. A suppressor does add a lot of gas and a DI gun is gas sensitive, some concessions need to be made or a little money should be spent on a Noveske Switchblock or like device.

you may have an op tempo which prevents you from a decent cleaning and lubrication regimen: Most of us who can pick and choose our guns don't have an op tempo. The guns mentioned above can still go 2,000 rounds without issue, or even longer. That should satisfy most TEOTWAWKI scenarios.

you do not have reliable access to really good "mil-spec" ammo: Lots of people are running cheap steel case in the above mentioned guns without issue, I can't speak to what one might find in Afghanistan or some other place like that, but I know what my guns can work with.

you find yourself shooting full-auto relatively frequently: Advantage piston converted AR, but I do suggest you check out one of the Knob Creek shoots to see what folks are shooting there. Lots and lots of DI guns on FA or SF lowers. Some of them are short and have cans on them.

Now combine any two of those points and you may need to put more thought into it.

If you want a gun that is piston operated, buy one that started that way and retain all of the features of a piston driven firearm.

For full disclosure I think piston converted AR's are piles of crap forced upon us to address shortcomings in AR's that were crap to begin with. All of their major selling points are refuted if you purchase a "good" AR from the get go.

[jslaker]

there are really only two companies that have put their guns into hard use service and had them work reliably. Hk 416, and the LWRC M6.

Interestingly, I've heard tell that the Norwegians have had less-than-stellar performance from their 416s. Apparently something about the sudden temperature change moving from heated buildings to cold outdoor environments can cause the piston system to start behaving funky on them.

[Odin Bravo One]

They certainly could be having problems when making an extreme temperature switch. There are all sorts of firearms that do not work as well at extremely cold temperatures, and going from warm to extremely cold only serves to amplify those effects. AI goes so far as to develop a special purpose sniper rifle for artic/cold weather environments due to effects it has on a bolt action rifle. It would stand to reason that the piston guns could suffer from some of the same issues. The DI guns don't work so great when it is cold either. I wouldn't attribute cold weather issues solely to one make and model.

[Dagga Boy]

Jay Cunningham is right on the money. I get asked this all the time. My response is usually that there are a couple of hundred guys in the US military that "need" a piston gun, and they have them.

I have run my DI AR's in head to head very high round counts against piston guns without issue. In the most notable case, a Ken Elmore built Colt L/E 6920 ran 1920 rounds shot as fast as the users could pull the trigger (64 shooters hand the gun off) while doing an Aimpoint demo. This was run next to an HK416. The only difference was that my gun was hot around the barrel, and the HK wasn't. Other than that, neither gun had a malfunction or issue. The reality, is most of will never have 64 guys from one of the premier SWAT teams in the country lined up with a 30 round magazine in hand to burn through their gun (most of the internet genius's will never shoot this many rounds in the life of their gun). I do stuff like this regularly, and all with DI guns. I am currently using Centurion Arms guns with a CHF barrel that has the MG chrome lining and are mid length gas systems for my demo guns. My previous LMT MRP demo gun has 30,000 rounds of very abusive use and is rarely cleaned and has never had any major issues. Again......I need a piston because....? The key to running a DI gun, is running a top tier AR and stay away from hobby guns.

I do love my Steyr AUGs, so I have piston guns if I need them.

[jslaker]

They certainly could be having problems when making an extreme temperature switch. There are all sorts of firearms that do not work as well at extremely cold temperatures, and going from warm to extremely cold only serves to amplify those effects. AI goes so far as to develop a special purpose sniper rifle for artic/cold weather environments due to effects it has on a bolt action rifle. It would stand to reason that the piston guns could suffer from some of the same issues. The DI guns don't work so great when it is cold either. I wouldn't attribute cold weather issues solely to one make and model.

Absolutely. I meant it more as a "hey, this is an interesting example that all guns can be tripped up" as much as anything. From what I understand, a lot of the griping amongst the Norwegians apparently stemmed from the fact that they generally didn't run into those issues as often with their old G3s.

I did a bit more digging after posting, and, lo and behold, it looks like they also had similar problems (http://www.thefirearmblog.com/blog/2009/03/06/norwegian-soldiers-having-problems-with-hk416-2/) with some of their DI C8s. :)

[45R]

I've had both DI and Piston AR uppers. I kept my DI and have sold my Piston rifle. I saw no added benefit to my piston rifle other than it shot a bit cleaner.

[P30shtr]

Jay Cunningham is right on the money. I get asked this all the time. My response is usually that there are a couple of hundred guys in the US military that "need" a piston gun, and they have them.

The only difference was that my gun was hot around the barrel, and the HK wasn't.
.


C'mon, nobody wants to get "burned":p

[DocGKR]

While initially excited by the piston concept, over the last 5 years, I have come to the conclusion that 90% of users will be better off with a quality 16" mid-length DI AR15. In addition to Colt, DI rifles by BCM, Centurion, DD, KAC, LaRue, as well as LMT and Noveske (those w/a true 5.56 mm chamber) all run well. The highly esteemed, extremely experienced Pat McNamara recently mentioned that he prefers a 5.56 mm DI 16” barrel AR15 with a long FF rail and a RDS (w/flip up 3x magnifier as a useful addition) for the majority of his carbine use, including indoors for CQB; he specifically mentioned LaRue and DD AR15’s as working very well for him. Kyle Defoor mentioned nearly the same thing in a recent class. I fully agree with them and run almost all my carbines the same way:

http://www.tridentconcepts.com/alumni/Portals/0/NTForums_Attach/148365765671.jpg

[ADKilla]

While initially excited by the piston concept, over the last 5 years, I have come to the conclusion that 90% of users will be better off with a quality 16" mid-length DI AR15.

Concur. While the rage now a days is tacti-cool, a good DI AR-15 with a light and a RDS will solve most of your problems. Even when I was in the sand boxes of both Iraq and Afghanistan, my USGI M4 ran fine; and that was a government issued weapon and very fine sand that got into everything. For most civilians who will never see the desert of the Middle East, a quality DI gun like the S&W or Daniel Defense will be fine for you in normal settings.

[will_1400]

I agree with DI being a good system. Granted, my experience with ARs thus far is being issued a beat-up M16A2 during my fam fire/quals at CATM, but considering the only problem I had was my dumb ass accidently grabbing an empty mag during a reload, my experience was positive.

[Failure2Stop]

Concur. While the rage now a days is tacti-cool, a good DI AR-15 with a light and a RDS will solve most of your problems. Even when I was in the sand boxes of both Iraq and Afghanistan, my USGI M4 ran fine; and that was a government issued weapon and very fine sand that got into everything. For most civilians who will never see the desert of the Middle East, a quality DI gun like the S&W or Daniel Defense will be fine for you in normal settings.

Unless you have a need for instantly changing from suppressed to unsuppressed with a 12.5(-) barrel, a quality DI AR will not only be fine, but wholly acceptable, and in many criteria better.

[jslaker]

Unless you have a need for instantly changing from suppressed to unsuppressed with a 12.5(-) barrel, a quality DI AR will not only be fine, but wholly acceptable, and in many criteria better.

Only other exception I'd throw in would be sustained full-auto fire -- ostensibly the reason for the IAR being based on the HK416 -- but the average shooter doesn't have access to FA lowers, so that's pretty niche as well.

[Failure2Stop]

Only other exception I'd throw in would be sustained full-auto fire -- ostensibly the reason for the IAR being based on the HK416 -- but the average shooter doesn't have access to FA lowers, so that's pretty niche as well.

The fact that two Colt submissions (both DI) made it to the final cut on the IAR selection prettty much killed the argument in my opinion.
Piston systems do not appreciably drop chamber temperature below DI systems, the real cause of cook-offs.
The IAR was chosen due to it's performance in relation to a needs document, not because of its operating system. It is significantly different than an M16/M4 in many more areas than just operating system, and all of those changes contribute to its success where others failed.

[will_1400]

Aren't the problems associated with excessive chamber heat in DI ARs caused mainly by people using an AR like an LMG instead of a rifle?

[Failure2Stop]

Aren't the problems associated with excessive chamber heat in DI ARs caused mainly by people using an AR like an LMG instead of a rifle?

That's the point of the IAR.
Feels like an M4, puts out a lot more lead.
Lots of ways to contribute to the success of that application, but weight reduction is not one of those.

I have shot M4s to the point that they had cook-offs.
6 mags in less than 5 minutes will get you there.
Drop that to 4 mags in the same time and you will be ok (non-SOCOM thickness barrel).

IARs will push more, and the op system helps, but it isn't the only factor.
There is also a change in application. The IAR is not an LMG, its an Automatic Rifle, and it has to be shot as such.

[will_1400]

Gotcha. Thanks for the explanation.

[jslaker]

The fact that two Colt submissions (both DI) made it to the final cut on the IAR selection prettty much killed the argument in my opinion.
Piston systems do not appreciably drop chamber temperature below DI systems, the real cause of cook-offs.
The IAR was chosen due to it's performance in relation to a needs document, not because of its operating system. It is significantly different than an M16/M4 in many more areas than just operating system, and all of those changes contribute to its success where others failed.
I was honestly thinking more gas tube than chamber temp.

ETA:

FWIW, it's my honest suspicion that the HK416 was chosen for the IAR because someone in the Marines wanted a backdoor way to field HK416s than any inherent advantage to the piston system anyway.

[Jay Cunningham]

FWIW, it's my honest suspicion that the HK416 was chosen for the IAR because someone in the Marines wanted a backdoor way to field HK416s than any inherent advantage to the piston system anyway.

I think maybe F2S has slightly more insight into this than his honest suspicion.

Um... yeah.

[LittleLebowski]

I think maybe F2S has slightly more insight into this than his honest suspicion.

Um... yeah.

Yup. Which is why he's an SME here. Folks, listen to him when he speaks.

[Failure2Stop]

FWIW, it's my honest suspicion that the HK416 was chosen for the IAR because someone in the Marines wanted a backdoor way to field HK416s than any inherent advantage to the piston system anyway.

It's my "strong suspicion" that the IAR was a way to give a more appropriate platform to users when the only official option was the M16A4, which is only slightly more cumbersome than a fence post and is neutered by 3-round burst.

[fuse]

It's my "strong suspicion" that the IAR was a way to give a more appropriate platform to users when the only official option was the M16A4, which is only slightly more cumbersome than a fence post and is neutered by 3-round burst.

Interesting to hear that full auto is acceptable, again.

Perhaps we're in for a new era of spray and pray, with awesome new hardware that can keep up?

[DocGKR]

"Perhaps we're in for a new era of spray and pray, with awesome new hardware that can keep up?"

Or perhaps we are in for an era of well trained and qualified individuals who know when and how to properly use full auto fire...

[will_1400]

IIRC, "spray and pray" was the standard approach when the Army adopted the M16 back in the 60's, the philosophy being that if you put enough fire downrange, you're bound to hit something eventually.

[Failure2Stop]

IIRC, "spray and pray" was the standard approach when the Army adopted the M16 back in the 60's, the philosophy being that if you put enough fire downrange, you're bound to hit something eventually.

"Spray and Pray" has never been doctrine, a training step, or an accepted TTP. It is the response of a scared conscript with little training in an alien environment when being shot at by a hidden and sneaky enemy.
There most certainly is an application of suppressive fire to enable maneuver, but that is something else.
There actually was a study that pulled data from WW2 and Korea that pushed us in the 5.56 direction, in which the data indicated that whichever side of a meeting force shot more rounds (regardless of caliber), was usually the victor. Interesting ripple in small arms development and employment, certainly, but it did not start a training cycle of "Point toward loud noises and pull trigger until magazine is empty".

[will_1400]

Alright. Chalk another one up to bs rumors being spread around. Thanks again for the info.

ETA: To clarify: I'd read and heard from multiple sources that full auto was highly encouraged on the grounds that I stated in my previous post.

[jslaker]

Well, color me thoroughly corrected, then. :)

[l8apex]

My small sample of data has been positive with the M6A2 LWRC, as well as a few other fellow shooters. 5000+ rounds without a hitch. It is not to say that a DI wouldn't do the same, as I full confidence in my Noveske as it too has been the bees knees. The LWRC is the 'beater' rifle for me. The weight is noticeable compared to the Noveske.

[ffhounddog]

Question then, why is my 14.5 lwrci M6 with DD rail lighter than my DD lightweight 14.5 everything is the same Compm4, troy rears, fixed fronts, h2 buffers and vltor modstocks?

Even balances better too.

[Failure2Stop]

Question then, why is my 14.5 lwrci M6 with DD rail lighter than my DD lightweight 14.5 everything is the same Compm4, troy rears, fixed fronts, h2 buffers and vltor modstocks?

Even balances better too.

Because it's full of hot air?
:D

[ffhounddog]

Hot air does make things lighter. Thanks

[Failure2Stop]

Seriously though, it is interesting that your LWRCI is lighter than your LW DD.
What handguard and length are you using on each? And how do the barrel profiles compare?
I'm not trying to troubleshoot your weight disparity, just interested in how they are comparing.

[ffhounddog]

Seriously though, it is interesting that your LWRCI is lighter than your LW DD.
What handguard and length are you using on each? And how do the barrel profiles compare?
I'm not trying to troubleshoot your weight disparity, just interested in how they are comparing.

7.0 Daniel Defense Omegas.
Barrel on the DD is LW and the LWRC standard
TD full size grip on both but the DD is a QD version
TD pistol grips
Vltor Modstocks
Troy rears
LWRC has a Larue mount for the CompM4 and the DD has a CompM4 in a Aimpoint mount

That is the only difference.

[Failure2Stop]

7.0 Daniel Defense Omegas.
Barrel on the DD is LW and the LWRC standard
TD full size grip on both but the DD is a QD version
TD pistol grips
Vltor Modstocks
Troy rears
LWRC has a Larue mount for the CompM4 and the DD has a CompM4 in a Aimpoint mount

That is the only difference.

Huh.
What's the weight difference? (assming you put it on a scale)
Or is it perceived weight/balance? (which I also understand, as I have never weighed any of my weapons)

[ffhounddog]

It is a perceived weight difference. It might be more of a balance issue.