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. 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.