What are the pros and cons of DI vs. Piston gas systems? I wanted to expand my knowledge on the two. I know that piston gas systems are great for ARs that fold, but not much else.

Well, in before the haters that say DI is just as good.

My piston gun is the cleanest running of all my guns.  Maybe a coincidence, maybe not.  But I can literally put a thousand rounds through it in a weekend shoot and I can still easily tell what color the bolt carrier is.

They are in general heavier.  Mine is <6lbs, but it has a CF barrel and handguard.

they have proprietary parts.  Haters like to point this out while saying KAC is best at the same time...so hypocrisy is of course present there as well.

Not sure one is better than the other.  I would buy either and be happy, but I'd not buy either a piston or a DI gun as a criteria of what I'd be looking for, if that makes sense.

Piston:
More expensive (usually), heavier, shoots smoother and cleaner, most gun shops don't carry parts,

I realize this is in the piston sub forum so I am sure I won't make friends here, but I am leaving my 2 cents regardless.

Firstly, the gas system has nothing to do with folding stocks. Due to the construction of the AR15, generally speaking, there are no folding stocks. Folding stocks are achieved by moving the recoil spring elsewhere and enclosing the bolt in the receiver through the full stroke of the bolt group. The AR15 requires the buffer tube because the bolt needs space to move backward and the tube houses the recoil spring. This is completely independent of the gas system. The gas system simply diverts gas from the barrel to the action. A hinge on a stock works no better on a gas piston than on the DI.

This usually becomes a game of "what do you own". I am a through and through DI guy. I like my $10 gas tube that is not proprietary and can readily be replaced by visiting any gun store. I like that it isn't proprietary, there is no compatibility issues with any other companies handguards, barrels, bolt groups or uppers. I like that my gas system is one part. I have yet to find a piston system that does anything better than my $10 gas tube. People like to talk about cleaning but that myth has been beaten more than Rihanna. Googling "filthy 14" is just one of many stories.

The real dirty little secret is that the AR15 does in fact have a gas piston anyways.

I prefer DI personally for the AR15. Of course the AR18 is a fine piston design. Love the Steyr AUG and it's basically a bullpup AR18. Many other designs copy the AR18 gas piston system. Of course the AR15 design continues to be the master. The HK 416 is the best piston AR15 platform no doubt. The LWRC isn't bad either. But I still prefer my AR15's to be DI since that's how it was originally designed. It's lighter, more accurate, and suppresses better. But pistons allow the gun to stay cleaner and run longer without cleaning. Downside is there's more parts that can break. Of course full-auto mag dumps the piston is better as the DI gas tube will melt.

Kind of my take as well.  The Henderson Defense thread where he runs guns to exhaustion was interesting, because basically the DI guns way outlasted most AR15 based piston guns, which broke and wore out faster, at their machine-=gun rental range.  I think the HK one's did better than most though, at least.  Obviously purpose made Piston guns are a different matter, and the AUG is an excellent example of a pretty great piston gun; which was designed ground up to be a piston gun.

As to the concept of piston, to me it's a step backward in technology evolution, not forward; as the DI system is the more efficient and advanced system.  It's intended to be lighter, for an infantry light arm.  That said, if I'm running a short barrel with very heavy sustained high-rate fire, then piston has appeal.  Nobody makes a belt-fed MG in DI.  Is your gun going to be a belt fed MG?  IMHO, most piston AR's were made differently, for the sake of being different, so you could have something differentiating to sell - TBH.  That said, the claims that piston are less accurate inherently, hasn't really come to fruition in reality, IMHO, as most piston AR's actually shoot pretty accurate.   Mechanically, my problem with Piston is that it's not what the AR system was designed to be.  The BCG is getting an off-center force on it to recprocate, with most pistons that just whack the top of the BCG; whereas DI puts all the force in the middle and in alignment.  The receiver of an AR if soft aluminum.  That will last longer than an AK receiver does (Henderson Defense data again), because there's no wear or force on the aluminum receiver in a DI system where the force vectors are all balanced.  In a Piston, the BCG force on the top, has to have a counter force of the receiver itself, to keep it moving.  Which creates wear.  

If you want an SBR set up for sustained heavy full-auto rate fire - Piston has some appeal.  For anything else, DI has proven to the design with staying power, and frankly the piston craze has kind of faded like the .40 cal; by quite a bit.  based on all of that.  Exotic parts for no real benefit, and sometimes problems.  At heavier mass and higher cost.

JMHO; I know it's insufferable for some ass to come into a subforum and kind of talk smack.

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I've noticed this on all my piston ARs and people say I'm crazy.

DI just all around the best choice for most people.  Piston has advantages I know.

With the Superlative Arms DI gas blocks and a decent gas bleed off setting you will be running nearly as clean as piston. I think DI is better for tuning lighter recoil as you can run lighter carriers, buffers, springs and adjustable gas blocks. I have shot some really lightweight builds like this with very little recoil and excellent follow up shots. I also agree with parts availability. So DI definitely has its strengths.

I also run the Superlative Arms piston conversions as well. With that said I find the Superlative Arms piston easier to maintain. I just remove the op rod and do a little scrubbing. No pipe cleaners or anything like that. Its also nice to visually inspect everything and not have things covered up like with a gas tube. With a roller cam pin it also runs a bit smoother. I do find  the recoil impulse a big longer into the shoulder, its not as crisp and light as a DI gun can be if tuned properly. Spare parts as mentioned above can be a problem. Better have spares, you might not always be able to special order them. With DI you could probably barter for that kind of stuff.

I like them both, but I prefer piston.

This right here.  I have three pistons and one DI (Two ADCOR and one LWRCI). The pistons run cleaner, but I do have to pay attention to the front gas block.  I've had carbon foul it up pretty good.  The carbon has to go somewhere, and it tends to collect in this area.

I home brew my stuff with superlative arms short stroke kits. They've been the most problem free systems I've ever had. I strongly prefer the piston over DI for a gun that's going to be in harsh or sandy environments. My mk18 gums up just for seeing the outside air.

A DI is a piston. The piston is just internal to the bcg instead of being external.

I have a Sig 516 and it is the easiest to clean.  Yes, it is a bit heavier, but I do not notice the added weight, and I agree it is a smoother shooting gun.  Almost no recoil.

I have DI guns, but this past year I tended to shoot my Sig much more.

Thanks for your valuable input.

I hate to be an argumentative type, so don't take this as arguing.  I disagree with the assessment that DI guns are better for tuning lighter recoil.  You can run light weight BCGs in a piston with an adjustable gas system.  The Superlative piston has the same adjustable gas as the DI system.  I can tune mine to the point where I can literally feel the BCG cycling in the extension and it doesn't bottom out at the back.  You can make the same adjustments to a piston as you would with a DI.  It may be more difficult to get the lightest of light weight BCGs, but they do exist and if you're creative, you can get a piston "gas key" replacement that will work on any DI BCG on the market.  If you're going to the level of being that custom on a DI system, you can certainly get there with a piston just as well.  (I'm avoiding the whole DI is a piston thing because we all know that.)

As for weight, the difference is SO minimal that I still don't understand why people even mention it.  Especially on the Superlative system.  Literally the only difference is the hollow gas tube vs solid piston op rod.  So grams.  When compared to the difference between a gov profile barrel and a pencil barrel....  You wouldn't even notice it.

Here's my 2 cents.  Proprietary parts is certainly an issue.  Particularly with differences between the brands.  You can't even use an AA BCG in a Superlative gun or vice versa.  With that said, piston systems break less.  With all of the heat and stress taken out of the equation and vented at the gas block, the bolt, carrier, trigger group, etc see less heat and stress.  They still see the cycling stresses, but at a much lower temperature and without the heating cooling cycles.  Reduced metal fatigue means longer life.  So in theory you will see fewer breakages on a piston system than on DI.  So while they are proprietary, you're less like to need to repair them.

You don't have to worry about dwell with a piston.

Get the one that makes you happy:)

I’m beginning to think of guns like shoes
Find the one that fits your best and makes you smile every time you put them on

Regardless of piston or DI, familiarity and training will win the day

this is a recurring thread.

Agreed.  I think it's safe to say that at this point the only real determining factor is personal preference.

I love my APC223 I cut down to 13", runs like an absolute dream.

Like people above said, pistons are clean, shoots smooth, a lot less gas while suppressed, and is heavy. I would also be out of luck if a part were to suddenly break on me until I got a replacement from manufacturer because you won't find parts in stores. Until I can procure a replacement part stockpile I'll keep training with my AR, but will hard swap once I do get it built up.

That's why you buy two!  LOL!

OK, more serious.  We should also make note that there are basically two categories of "piston AR".  

The style that isn't really based on the AR and isn't really interchangeable.  Things like the SCAR, APC223, IWI GALIL, Sig 5.56, AK variants, etc.  Rifles where the design isn't based on altering a traditional AR upper to have a piston.  

On the other hand, you have essentially AR piston conversions.  Where the only difference is the gas block, gas tube/piston, and BCG.  With these rifles, you can pop the upper off and put a DI upper on and keep moving or vice versa.  This would be POF, LWRC, AA, Superlative, LMT etc.

Question, what part of the gun is most likely to break?  More specifically, what part of the piston mechanism is more likely to break causing a stoppage on the rifle?  On a non-AR based system, kind of any part that breaks causing a stoppage is bad.  So if your recoil spring breaks, you need a new one and that's proprietary so it has to come from the manufacturer.  To my knowledge, you can't replace a Galil spring with an AR recoil spring.  So IF any of the proprietary parts breaks, you may be out of luck for a bit.

However, on an AR variant, the ONLY parts that matter are the bolt carrier (not even the bolt, firing pin, cam pin, or firing pin retainer), the op rod, and the gas block.  I'm assuming we aren't talking about a super custom tuned rifle that can only shoot one special hand load....  Anyway, if the recoil spring fails, get a standard AR spring.  If the bolt fails, standard bolt.  Barrel fails, well that's a bigger deal, but still standard barrel.  The lower is identical to a DI gun, so anything on that breaks and you just replace with the same parts.  You don't have gas seals on the bolt and the tolerances are irrelevant because the seal isn't important.  The BCG is actually a little stronger because the strike face is normally a solid piece of the carrier.  So, you'd have to break the carrier, the op rod, or the gas block.  And since there isn't any heat on the carrier, that's less likely.  The gas block is maybe possible, but you'd really need to hammer that to break a gas block.  The op rod is the most likely spot that would break.  So if you're really concerned, buy a 6 pack and you're good.

I guess where I'm getting at is, if you have an AR variant piston gun even though the parts may be special they aren't like to be the parts that will actually break.  And the ones that do are more likely to be the same parts that would break on a DI version.  I've had two piston rifles break and both times it was the receiver extension (buffer tube) that I replaced with a trip to the store.

Piston systems trade cleanliness for heat.

If you plan on running a few mags to clean out the cobwebs, you better wear a glove cause it gets hot AF.  

If youre running with a can, Id run a piston gun, If I was running it otherwise, Id want a DI rifle just due to how fuckin hot the handguard will get.  

If its full auto, you can afford to deal with heat.

AR piston system was a solution in search of a problem. Literally.

“Shoots smoother”… which is why you see exactly nobody running piston AR’s competitively.

SOF are pretty competitive one could say.

They certainly aren’t running them because they “shoot smoother”.

When people who have virtually unlimited choice are building out guns in order to chase hundredths of seconds and demanding the smoothest operation possible for fast follow up shots an external piston isn’t even a consideration.

This is not true.  Andrew and Becky Yackley (and their kids), Mike Sexton, Ryan Muller, etc.

Adams Arms has a competitive team.  Frequently they are in the top 5 finishers in multi-gun competitions.  Of course, no one can beat Josh Froelich right now.... LOL.

And not that I'm "anybody", but I compete with piston guns.  Used and Adams Arms for years until I built my Superlative last year.

That said, "smoother" is subjective and my personal belief is that they are all same same.  If the rifle is tuned to be smooth, the gas system isn't relevant.  Ultimately the response of a rifle to recoil has little to do with the way the gas runs and more to do with reciprocating weight, overall mass, and any potential muzzle appliance.

I'm sure fudds say the same thing about Glocks and .308 Win.

Not to burst to much of a bubble, but keep in mind that the top competitors are usually sponsored (not paid, but given heavily discounted or free gear) to promote their products.  And the difference of hundredths of a second rarely means the difference between winning and losing over a 2-3 day match.  Normally the top competitors are separated by seconds.  I just looked up the Big Tex Multigun Championship and the difference in time between 1st and second was 25 seconds. With penalties the difference was 40.  So more likely it's just not a thought.  Bottom line, the piston isn't going to win you a competition.  Sure.  But for a lot of people, that's not why we choose pistons.

I am a high level competitor and I live in that world every day. How smooth your rifle is running makes a huge difference. You’re not getting that with a piston.

Oh shit, where do you compete and for who? I always wanted to get into this style of shooting but live in Alaska :\
Do you have pictures of your kit, I'd be interested to see what I learn from it.

Seriously?  I live in Alaska too!  Birchwood has a monthly 2-gun and 3 gun match.

Birchwood like the housing complex? I live near Fairbanks.

edit: oh chugiak, I will have to check that out this summer

True, but you're also not not getting that with a piston.  My point was only to say that people do compete with piston ARs.  But smoothness isn't granted by the piston I agree.  Too many tribal knowledge myths are out there about what piston does and doesn't do.  For my part, I see no difference in anything DI or piston regarding weight, accuracy, or recoil.  Six of One, half dozen of the other.  Piston keeps crud out of the fire control group and runs cooler on the BCG.  Trade off is hotter at the gas block.  I tend to walk away with a sooty hand after a match.

There is a small contingent of multi-gunner in Fairbanks, but I don't know where the compete.  I'll find out.  I know the guy who basically runs USPSA in AK and he does a lot of multi-gun also.

There is usually an AK State Championship at Birchwood (Chugiak) in the summer June-ish.  If you're down in the area, let me know.  I'd be happy to help you out anyway I can.

I have multiple ARs… piston and D/I. Both will run, if you have a quality setup.

Only folding setup I have is a LAW Tactical folder on my truck gun… which happens to have a 11.5” AA upper on it. I could take that upper, pop the pins and swap in my 11.5” D/I upper… and it would work 100% (double checked… both lowers had H2 buffers). I’m not a huge fan of folding adapters, but since I want to run a suppressor on that AR pistol… I figured shortening it up would be beneficial. I’m planning on getting a dedicated locker for my truck… and if I can run it without the folder… I probably will pull it off.

I like piston setups, specifically AA’s setup, for suppressors. I’m not a fan of adjustable D/I gas blocks or bolt carriers. To me, I like changing a setting on the gas block, and it venting off more gas so it isn't running as hard. Only issue with an 11.5” barrel… if I run the Griffin Taper mounts, I cannot pull the gas piston out of the the gas block. I’m going to get another A2 flash hider, and swap so I can run an A2 adapter on my suppressor.

Now, most of my ARs have either an A2 flash hider or a Griffin muzzle device so I can run my can on them. D/I and piston… across the board. Suppressors will run with D/I… but I know it will be more gassy than my pistons. It is what it is. Just I opt for the piston guns if my can will be on it.

I’m not one that has a feeling that one is superior to the other. My 11.5” D/I upper has been 100%, and I’ve put some rounds thru it (runs with a Fostech Echo trigger). Only factory built AR I own is a Colt 6920… everything else was a lower built by myself and an upper either custom made or factory produced. My first D/I setup was a Macon Armory .45 ACP build.

Not an attack, just an fyi.  I have multiple AA pistons and just wanted to let you know that the AA system doesn't vent gas off.  The adjustment restricts the amount of gas allowed through the gas block but it doesn't vent any of that off.  I maybe misunderstood what you mean.  The Superlative piston system allows you to choose between a restriction type or a venting type.  When you operate it as venting, it diverts a portion of the expanding gasses forward away from the piston which has the effect of reducing the pressure on the piston.  It's a subtle difference.

People who say external pistons run cleaner I don't agree. While I do agree the bolts and chamber runs a bit cleaner, the gun gets dirty. You could spend about the same amount of time cleaning a internal piston or an external piston depending on your level of effort.

I cleaned my share my external pistons and internal and the amount of time to clean either is about the same with my level of comfort in cleaning.

It's the same reason that many competitive shooters use Glocks instead of the really high end pistols like a CZ75 or 1911. You have to spend a crazy amount of money to get it fine tuned. But with a glock you can easily put together a great shooter for about the fraction of the price.

An DI/internal piston is about the same. You could buy really cheap parts but to fine tune a piston, you just have to hope the manufacturer that made it can help you out or you find a great one. Also, if you're into competitive you're going to shoot out your AR barrel and most pistons, outside of something like AA, you need a proprietary barrel setup.

You don’t see a lot of Glocks outside of C/B-Class shooters at locals.

As someone that shoots CZ’s competitively, I’m curious what tuning you think they need?

I didn't say that. I said you pay a premium so you don't but at the same time you can't find parts and if you do sometimes it is a drop in and sometimes it isn't. I own 3 different CZs a Shadow2, 75b, and a parrot. They all are different with the parrot being the most different out of all of them. I have to go online and order parts for it such as new springs and so forth because my local shop doesn't have it.

Overall you're going to pay maybe 800 bucks for a basic CZ75b model but for the more gucci types you're paying about 1100 at minimum when you can buy a glock at 600 bucks and put a new trigger and sights on it and you're ready to go for the average shooter.

But that's not what this topic is about. I'm only comparing Glocks and AR15s in that parts are readily available and cheap to make it do what you want. For the OP it makes the most sense to get a really nice piston, then get a DI upper that you can fool around with. If you buy for example a LMT MARS piston type upper, such as the more recent estonian reference rifle, it's going to last you a life time and on top of that you can put a DI upper on it and not have to worry.

As for which is better, that is very subjective. You aren't going to wear out an AR15 internal piston just as much as you're probably not going to wear out a external piston upper.

As an example, I built my first internal piston AR15 (DI as people would calll it) back in 2012. I shot it a few times a month until about 2017 when I found Tulammo can be bought for about 150 bucks per 1000 case. I was shooting all of it per month until about my 10th case when it started to keyhole. That means I shot about 9000 rounds out of it plus some more if you count what I shot between 2012 and then, and it could still shoot just fine if I used a heavier 77gr. The throat was mostly gone on the barrel and was at the 9th ring when I put a throat gauge in it but I have no reference on the first measurement so I don't know how many ticks it went down.

Overall DIs are tough, and pistons are tough. Just buy whatever and shoot it and not worry about what is better or not. If you plan to shoot in the 1000s of rounds, which is very doubtful for most people because I don't even shoot that much any longer it was just one point of my life. I wish I could but overall if you shoot 100-200 rounds per session and shoot once every couple of months, your rifle will last forever. Assuming you shoot approximately every 10-20 seconds and don't overheat the barrel your barrel could last up to 12000-20000 mark without issue and since you're only shooting <300 yards, you won't notice any accuracy problems unless you're benching it. A .223/5.56 will wear out any barrel regardless of the gas system it has and some pistons, such as POF tend to have a specialized chamber cut that is supposedly going to make it last just a little longer. Very subjective and very depending on how you shoot and how hot you get your barrel.

Just buy a PWS and be done with it.

This.

yup

Just going to leave this here...



And since this isn't GD...

I do feel that my PWS (piston) runs cleaner, though it's a little heavier. I like the recoil feel better. I have lighter DI's. I do like the DI's for the fact that I could find parts easier if things ever went sideways and had to rely on "pick ups." I didn't use to think that was a big deal but the last 3 or 4 years have slowly changed my mind.

Both systems are fine and will work for most of us without noticing a difference.

Both systems have adjustable gas blocks available and can be tuned to shoot equally smooth.

Piston guns use A FEW proprietary parts (gas block, bolt carrier and op rod in place of a gas tube). Same barrels, upper, bolt and in most cases handguards.

Piston guns do not damage upper receivers or require different barrels to run.

DI guns may be easier to find parts for, especially if we find ourselves in a SHTF scenario, but not if you mod the crap out of your gun with a ton of non mil-spec parts. In such a scenario, most piston guns can be converted back to DI fairly easily with hand tools (heavily modded DI guns can be turned back into mil-spec just as easily).

DI systems crap into the receiver every time you pull the trigger. Sounds worse than it is though. With a good nitride or ENBN BCG, all that carbon just wipes off with very little effort.

DI guns can clear the receiver of debris (mud, sand, water etc.) by using that pressure wave/blast of gas to push it out of the receiver and magazine. That's a huge advantage DI guns have over their piston brothers.

Full disclosure: my go-to is a basic, slightly upgraded from mil-spec DI gun. I trust it 100% and believe it will stay solid for many thousands of rounds, regardless of the conditions. My BO pistol is a piston gun and a safe queen/range toy. Once it has enough ammo through it to be considered solid, it may take on a different role though.
Sorry for the essay, but I did a metric ton of research on this topic before building my BO.
Hope this helps,
Gator

I'm not sure that's unique to DI guns.  I get the theory, but in practice, the blast of gas is contained internal to the BCG until it vents out the ports as the action opens.  But that vent happens through the ejection port.  I don't think much of any high pressure gas is vented into the receiver.  That's why the build up of junk in the trigger group area is slow and takes a long time.  The carbon build up you normally see is in the BCG mainly.

My point is, it's possible that the clearing of junk from the receiver is a result mainly of the high speed action of the BCG more than gasses.  Which would mean both have effectively the same advantage.  Would be interesting to see if that matters.

20 years ago short guns did better with pistons

In 2022 shorty DIs have come a long way.  DI is now as reliable, cheaper, lighter, less recoil, and less moving (proprietary) parts

There’s no real benefit to a piston on the ar platform anymore

I’ve owned and carried 416s.  I don’t own any anymore.  They’re cool but not worth all the above BS