I hear this posted frequently, that you should only consider a piston AR if you are going to do a suppressed SBR. Why is that?

With a suppressor the big benefit is that piston guns stay much cleaner.

No they don't.   Suppressors foul every operating system equally.

Mostly, from experience.

Short answer is that it's not necessary - tens of millions of rifles run just fine on DI, and they're cheaper and lighter.

If you happen to run crappy ammo, or have an SBR or suppressor, where a lot of particulate residue can make it back into the receiver, then a piston helps stop some of that, at the cost of other drawbacks.

Suppressors act like sponges an often create low gas situations that result in short cycling or not cycling at all. The piston can usually over come that. That's why people say what they do. You don't normally need them in a 16" or longer suppressed rifle unless you're running light loads.

Da fuq?

I'm dumber for having read that.

Agreed...

Most of the time suppressor cause the gun to become over gassed. To fix this you can use heavier buffers, adjustable gas block,  adjustable bolt carrier. There are very few suppressors that don't cause this but there are some.

No.

Thanks. I completely get that piston ARs aren't "necessary" but I really didn't want to get into that in this thread. I was just more curious about the statement that I have read and heard a few times that you don't even need to consider a piston AR unless you are doing a SBR and/or suppressor. Was just curious why that was and the physics behind it, or if it was just one of those old internet rumors that keeps getting repeated because it is on the internet.

I will say if your a left handed shooter and shoot suppressed piston AR-15's are great way to lessen gas to the face. But you could just have a left handed AR or one other ways to reduce the gas as I previously posted.

Honestly a lot of it is just because a person heard it on the internet and repeated it. Some truth to it when it comes to stacking SBR (Depending on length) with a can due to dwell times and bolt wear/abuse. The shorter the gas length of the AR, the harsher it seems to be on the system/bolt and the more the dwell time is screwed with. A piston doesn't typically have this issue as it can be tuned a bit easier with adjustable gasblocks and the like. The traditional stoner gas system does have adjustable gas blocks as well, and carriers but they aren't as maintsream as adjustable blocks on piston setups. (See SCAR/LWRC/PWS/POF)

Shooting a suppressed rifle is going to get fouled fast, no matter if it is an external piston, Stoner Gas system or even if it was for a rifle "designed" to be piston.

Had a SCAR 16S for a bit that I shot suppressed near exclusively and the damn thing got dirty fast. The entire inner of the upper receiver on the SCAR would turn from FDE to a black from the amount of blowback from the barrel. That's what seems to be forgotten in this, the extra blowback isn't from the gas fed back into the Stoner Gas system of the AR but rather from the bore. You can't really mitigate this much, save for delaying the unlocking of the bolt (Which is what adjustable blocks/increased carrier mass/buffers attempt to do). Even then, you're still going to get a lot of blowback from the bore.

I've shot PWS/LWRC/SCAR all with the same can and all with adjusting the gas blocks to the proper suppressed setting. Each got just as dirty as my Daniel Defense. The setup that had the least experienced blowback to the face was the SCAR but that is due to the design of the receiver. The cut out on the AR15 charging handle will bleed a bit of gas from the bore shooting back into the receiver, just will always happen.

Because they regurgitate wrong information an “expert” spouted a decade ago.  Pistons aren’t some magic device that don’t foul the gun.

Thanks, that is what I thought. So it seems the piston is really no better or no worse than the DI then. So in that regard, it really just comes down to preference and if one really wants a piston bad enough to make that move into a piston AR over a DI AR.

Not sure if serious or trolling?

i'd agree with that and in fact i prefer to NOT use my piston uppers with cans because then i am cleaning a rifle that otherwise DOESNT need much cleaning.

DI gets dirty anyway, so i might as well shoot those suppressed.

as for the left handed thing, i'm a lefty and i just dont see all the fuss about DI uppers putting gas in your face without a can. i never notice it.

i do notice the gas from shooting suppressed with either system and as a lefty it sucks.

ehhhh I don't agree with this statement.  My DI guns are much dirtier in the lower receiver than my 2 piston guns after running suppressed. After shooting my DI guns suppressed it is a bitch cleaning out the lower receiver around the trigger group.

Curious, you using any mitigation attempts at the increased velocity/decreased unlock time on the system or are you just throwing the can on and shooting it?

I've found that when I stepped up to a higher buffer/adjustable carrier/adjustable gasblock that the lower doesn't get as fouled. My piston setups still get fouled in the lower, if they are a non-adjustment based is why I ask.

When shooting suppressed the majority of the gas in the receiver comes through the chamber, not the gas tube. Having a piston doesn't change that.

Out of curiosity, has anyone ever did a round count between the two to see how long each system will run (suppressed) before the need of oil?
Or to see how long each system would run suppressed without oil?

Not even close.

This was my initial thought.....

I used to shoot a 16” 7.62x39 piston AR suppressed with no problems and minimal lube, then converted it to D.I. and ran into failures because of the fouling after 40 rounds. Had to clean the bcg and run it wet. When it was a piston setup, I could go well over 200 rounds without cleaning or relubing and gas from the charging handle was barely noticeable compared to D.I.

I run piston because I like to breath while shooting suppressed.  On my DI AR, I can only fire a few rounds before I choke.

It sounds like you guys sure clean your rifles often.  Lube it and shoot it.

I like my piston guns because they don't completely shit up my lower receiver with gas and filth.

I will agree, my LMT piston BCG gets very dirty when I run it suppressed.  When the gas can't go out the front end, it's going somewhere.

I have heard a lot of WAS (wild ass shit) in my time, especially from the Academny Sports "gun experts", so I believe who ever posted this is serious

You get a ton of extra back pressure when you put a suppressor on a DI system.
Blows a lot of debris and gas back at you through the charging handle slot, and ejection port.
This becomes even worse when you run a shorter barrel.

With a piston setup the gas is kept up front, and often has variable settings for you to tune the gas.
Alternatively, if you install an adjustable gas block on a DI gun you can also tame the gas to a certain extent.

You get an extended pressure cycle with a suppressor regardless of the operating system it's on.

The only thing that dictates how long the pressure cycle lasts is the engineering of the suppressor itself.

Some suppressors like the newer Surefire SOCOM cans are very well designed to reduce this issue whereas older legacy suppressor designs will hold and vent the pressure peak in the system for a longer period of time (relatively speaking) which is why when running those types of suppressors, the action gets just as dirty on a piston gun as it does on a DI gun due to the fact that the pressure vents both ways in the barrel and once the empty case is extracted from the chamber, half of that pressure and carbon blow through the chamber and into the action.

The only thing adjustable gas blocks do is allow the cycle of action to slow a little and allow a little bit more gas to vent forward and out of the muzzle prior to unlock and extraction of the spent case.

What makes the piston systems superior in this matter is the fact that they are not compounding this issue by blowing hot carbon into the action via the gas tube as well as through the chamber and the inherent fouling is greatly reduced as is the temperature, meaning lube sticks around longer as well.

I won't go with a piston system because I understand how a piston system breaks the mode of operation of the DI gas system.

Piston systems eliminate the backpressure that holds the bolt in place in the chamber after firing for a few milliseconds, allowing chamber pressures to drop to a safe level before disengaging the bolt and beginning the extraction cycle.

No AR should ever use a piston system.

I'm with Eugene stoner and Reed Knight on this one.

I really wish people would stop regurgitating this tripe.....

BINGO

My LMT pistons are no cleaner than the DI.  I don't care what the info-net says...

Because people for some reason equate all piston ARs with the HK416.

The HK416 has been used more or less since inception by extremely high volume shooters that were looking for a compact assault rifle that could be suppressed and fired on full auto. It has not been without teething problems and upgrades during its development, but most of them have focused on optimizing it for the role for which it is still arguably most heavily used (numerical use by conventional-Euro forces exceeds the number in use by SOF, but I sincerely doubt they use them harder, even combined).

This design, development, and service history is not shared by many (if any) other piston AR design. When the HK416 was newer, and there were fewer other piston designs, a lot of guys would just say "piston AR," meaning the 416. This has evolved into the "truism" that piston ARs are best suited to full auto, suppressed SBRs.

~Augee

I actually prefer a piston rifle because it runs a lot cleaner than any direct impingement system regardless of the barrel length. If it stays cleaner, with less crap to foul up the moving bolt and carrier, it is obviously going to run more reliably. The direct impingement systems vents all those hot gases and carbon directly into the bolt carrier group and only ignorance would suggest that this is a good thing or that a dirtier bolt carrier group functions just as well as a clean one. I have one piston upper and one original direct impingement upper receiver for my Colt M16A1 and I tend to prefer the piston upper. However I do shoot both. I have noticed, however, that using a suppressor with the piston upper does not result in a cleaner weapon because the suppressor vents a ton of that carbon and gases back into the upper receiver past the piston and can still foul up the upper as well as even venting gases into the magazine and magazine well. Without the suppressor and the M16A1 is much cleaner than the DI one even/especially when shooting full auto groups. And that's a fact.

Anyone who says PISTON ARs get just as dirty as DI are missinformed. If you shoot similar weapons with same ammo and same suppressor on a DI and PISTON, pistons will be much cleaner.

What it's being failed to be said is that there are 2 ways that dirty (burnt powder and smoke) gets into your system:

#1. Through the gas port (hole) into your barrel that pushes your BCG to cycle
#2. Through the barrel backwards after the BCG is pushed back and a casing is removed

The suppressor forces more gas to stay much longer in the barrel, increasing BOTH the amount of gas sent through the gas port to push the BCG back and the gas that lingers the barrel once the BCG opens gets pushed back into the system.

A proper piston system, will virtually eliminate the dirty/gas that comes from #1 into your upper/lower. This happens since it uses a piston rod to push the BCG (not gas). All that dirty is diverted from your upper and stays/gets exhausted within the piston itself in the front/mid of the barrel and not dumped in your BCG getting both your upper and lower dirty.

However, PISTONS do absolutely nothing to prevent the dirty that lingers in the barrel (which is increased with a suppressor), so for #2, the amount of dirty is indeed the same as DI. Once that BCG opens to cycle the bullet, the left over gas comes backwards into the system.

But saying DI and PISTON shoots just as dirty is inaccurate since DI pushes a lot more dirty through the gas port into the BCG getting your DI system way more dirty than piston.

Sigh.

I don't think Eugene Stoner and Reed Knight's opinion qualifies as "tripe", given that Stoner designed the system and he worked for Knight in his last years.

Your opinion, on the other hand.... to me, that's in the "tripe" category.  Far as I know you are an actual nobody in the field of firearms design.

Lol!  Like engineers can't be wrong.

Residual pressure in the system as the bolt unlocks is still more then the 9 or so pounds of pressure required to overcome the action. Otherwise there would be no wear on the rear of the lugs, no need for stronger extractors, extractor inserts, O-rings, whatever.... and replacing a bolt wouldn't bring a high round count, freshly out of tolerance headspace gun back to within tolerance headspace.

And by all means, link up to any data that actually proves this claim. Test data would be great.  Other then that it's an unverified theory and marketing claims.  Something both St. Eugene and Reed Knight were good at.

Theory is great, reality is better.

Piston AR’s are a waste of aluminum and CNC time. They’re not good for anything!

You're right. You absolutely shouldn't have one.

If you DO have one, send it to me for disposal.....

Do you know, how I know you don't own a suppressor?

My biggest issue with piston guns is they are louder than DI guns with a suppressor. Suppressors usually make the gun over gassed. Most piston kits come with an adjustable gas block which can be adjusted for a suppressor, but the same can be done on a DI gun.

Who cares about getting the gun dirty??? In the army we used to shoot blanks with adapters all the time. Now that is a dirty system!!!

I run my mk18 style build suppressed most of the time and am getting a pws Diablo (long stroke gas system” because of the gas in my face... it really burns the eyes. That’s the only reason I would ever consider a piston gun while shooting suppressed.

Well that and a piston gun on a 7 inch is a bit more reliable than a build...

This is an age old argument that will never be settled because few actually stop to analyze the key points.

Personally, I picked up a piston rifle because air was curious. I have a PWS Mod 2, it’s just as reliable &  light as my Knights Mod 2 with the same ammo.

Piston Guns only good on SBRs and suppressors
Is the same internet lore such as Hydraulic buffers don't last and
Anti-walk trigger pins don't do anything
If Stoner wanted ambi-controls he would have built it into the AR...

Oh wait that argument against ambi-controls which did exist here on arfcom
when I first signed up years ago (2006) which people on here would argue over
(Righties of course saying ambi-control not needed)...this view has obviously faded over time.
And now Ambi-controls are  a desired item on many ARs.

Hydraulic buffers... Even Kyle Lamb endorses them now
Anti-walk pins are not needed unless of course from super high round counts. The steel hammer pin from rotation
wears the hole out and flares the hole in the receiver. Until there is space for the pin to move around
leading to the hammer slipping off sear and rifle double and triple fires
(I had it happen with a lower) anti-walk pins fixed it. and will prevent this.

Piston guns only good for SBR and suppressor most likely just being repeated by
people who do not have any real experience with a piston gun.

Do DI guns work great? Yes
Are there numerous benefits to a piston gun? Yes
Depending on what you are looking for in a AR are there down sides to a piston? Sure
But as I have posted before, seeing how All U.S. and a majority of European Tier 1 units now run piston ARs
There is a reason for this... piston guns have a lot of advantages over a DI gun.

Augee just read your post about 416...I agree with you there.

^^^ Great stuff right there......

I bought a piston AR, shot a few rounds through it to "break it in", sighted in it with a new optic, and then ran it through a rifle/carbine course. Only one rifle failed in that class, and it wasn't my not-even-broken in piston-driven 16 inch AR. It must be garbage. I will try again this weekend to make it fail.

-shooter

say no more and the BS won't stack any higher.

Great post, Stukas87

This. You’ll just end up with a caked piston instead of a fouled receiver you can spray w oil

Unsuppressed maintenance is vastly superior to DI

I shoot both and I can't speak for everyone else but in my guns my piston is way cleaner and easier to clean than my DI guns. Does that matter? Not in a "fight" situation I guess. But when I am going to the range with friends and I know I don't like cleaning guns I usually take my piston because I will be more likely to clean it when I get home because it's easier. There is zero carbon inside the bolt because zero gas goes inside the bolt on a piston for example. Just clean off the piston and put it away and go back to the kitchen and have a sandwich.

Anyone that has ever cleaned both at the same time can not possibly say that it is just as easy to clean both. You can say that you don't care or it's not a big deal because that is subjective. But you can't say that it is equally dirty. That is objective empirically provably false.

Again does it matter for the purpose of what the gun was intended for? No, probably not. Not going to kill commies in a foreign land any better I guess. But if you (like me) want to spend as little time as possible cleaning guns after a day at the range then brother, you can't deny it is easier and quicker.

As for an actual potential benefit all I can relay is what I have been told from some guys I consider pretty smart on the subject. That would be that when the barrel length starts getting very short that makes it more difficult to have a reliable DI system. Shorter gas system length starts to introduce issues that Mr. Stoner could not have seen since he did not design the rifle to be that short. Remember he designed a rifle length system. Carbine and shorter came later. Who knows. He himself might have gone piston is the gas length got short. He never had the chance really.
Kind of like improvements to the 1911 after Browning died. Would he have improved the design and incorporated some of those things into his design? Maybe, we'll never know. But try to tell a 1911 guy that an external extractor is an improvement to a 1911. But make sure you are farther than arms length.

Whereas a piston kind of excels the shorter the piston gets. You don't see rifle length piston. Even in a rifle length system the piston would probably still be placed in the carbine location. No benefit to putting it further out on the barrel. Extremely short system = piston gets more attractive. The longer it gets the less attractive. But real world difference in war? Not that I can see.

Color me shocked!

I’m also a big fan of the guys who insist that a piston increases felt recoil. Apparently Gersch Kuntzman must have been firing a piston driven rifle