Let's get this out of the way immediately: I really don't want to start another "piston vs. DI thread here".  I am genuinely curious about what I'm going to ask.

Why do no new designs use direct impingement gas systems?  The AR15 is obviously successful and has "proven" that the system works so how come newer (i.e.: FN SCAR, Tavor, BREN 805/806, AK12, etc) designs are all piston-operated?  If the simple answer is that "pistons are better" then why are piston-operated AR15s not more popular (indeed, why are they so widely panned)?

It just seems odd to me that the AR15 should be so successful without having its gas system being copied even once.  

One problem with pistons in ar's is there is no common solution. Each company has their proprietary parts. One of the biggest attractions to the ar design is it's the lego gun, but the lego part goes away when I can only go to one place for parts. While there is certainly a lot of piston guns, they haven't shown a great increase for the cost. Now I own a lwrci ic and a FN scar but when you look at a 2k-3k price tag it gets hard to show cost effectiveness. The benefits are there but is it worth it for the price ? I think so but a lot of friends say no. I like the piston design across the board but most of the people I shoot with do not seem to see any major benefit for the price.

I know that the lack of standardization of pistons is a drag, but shouldn't there have been something by now that people across the board would be saying "THAT is the answer!" about?

Conversely, if pistons add cost but don't really add value, then why isn't there a DI version (or at least conversion) of the SCAR?

I was surprised m lock took off like it did. Getting anybody to agree on pistons is asking to much

There's a new folding AR coming out that is DI.

My theory:
Reason (1): Gun Mrkers Realized They Could Make an AR Somewhat of a Walled Garden with Piston Designs.
The DI AR15 is the equivalent of an "open source" design in computer software. Colt holds the patent and rights, but anyone can create, add, modify the code. In this case the "code" is parts. That's great for consumers - not so good for manufacturers.
Manufacturers have a vested interest in keeping a level of proprietary IP in their products so you can only come to them for replacement parts and upgrades.

Reason (2): No Royalty.
They can skirt certain rights and royalties due to Colt by making an AR derivative in such a manner that it in court, it would be hard for Colt to file for infringement and win a case. The operating system is dissimilar enough not to cross the patent.

Reason (3): Durability & Convenience.
The votes and the data confirms, operationally, piston guns have a number of benefits over DI. Piston guns don't need to be cleaned or oiled as often. They can operate easier in sand/mud/over the beach conditions. They don't spit gas in your face (or in the face of left handed shooters). etc. etc.




That also surprised me. Magpul did themselves a favor making the M-LOK system is a freely licensed platform - even to their competitors. Sign a no-fee license form before utilizing the M-LOK logo, get the design file specs, and go have at it.

Colt holds no in-force patent on the AR15 in general.
Patents expire in 20 years. Anything Colt had which generally covered the AR15 expired many years ago (over 30 years ago).
The reason there are so many proprietary parts is because so many companies have introduced improvements over the years.
I promise you the primary motive is not so you have to come to them for replacements, although that is a secondary effect.

We have a couple such as the HK 416, PWS, LWRC, POF but all are copyright protected, these systems have all proven themselves but again only they can make it where the di system is free domain. After those IPs go up we may very well have a new one. The scar is a different animal and is the best example of improvements that cost a lot. Is it a great shooter? you bet. Is it worth 3k. Hard to say. I mean 3 times better than a 1k ar no, but that's the concept of dimishing returns.

Theory 1 & 2, patently (pun intended) false.

Theory 3, eh.

Reality: a piston AR makes zero appreciable difference in 99% of consumer and military use cases while presenting larger negatives than simply cleaning your rifle.  Negatives to a piston AR you ask, well, luckily you already listed them in your Theory 1 & 2 as applying to the AR15/M4, but it's quite the opposite, saved me some effort there.  If picking a different rifle for standard issue, then, might as well go piston, but you likely have to handcuff yourself to that manufacturer regardless (if the rifle was made in the past 20 years based on patent term) whereas that is not the current case with the M4.

It seems that some manufacturers make piston rifles to differentiate themselves from the norm to sell rifles that would otherwise not sell.  Example: if POF didn't make piston rifles nobody would (well, most people wouldn't) pay 3++ grand for a incredibly picky to non-functioning AR just to be different.

Currently, I have two piston ARs, an LWRC and a PWS.  I previously had POF that I purchased only as a favor to a friend who needed the money - it took a lot of effort to get it to run acceptably, and by acceptably I mean I'd hunt with it or take it to the range, not put any real trust in it.

As for the first one of the two piston rifles I currently own, the PWS is only the upper, and it has issues with some lowers, specifically, the BCG is prone to sticking in the buffer tube depending on the lower due to the fatter end of the BCG in their "need" to mitigate BCG tilt or whatever.  It's currently on an Anderson lower with a PWS buffer tube, which works either because I can sort of tweak the angle of the buffer tube by way of the 3 set screws and got lucky when I installed it or because it simply has a larger diameter, I do not know.  The take away there is that providing some perceived "added value" on paper (if there's even any legitimate value added there in practice) doesn't necessarily translate to the interchangeability of parts even where it should.

As for the LWRC, the new revisions make for a fine rifle, I'd buy another.  Their short stroke design is superior to the piston systems in the PWS and POF, IMO.  However, they still suffer from the fact that depending on the part I can't simply just go pull one off another rifle.

With my "regular" DI guns, I don't have to worry about any of that shit (excluding proprietary handguard/upper receiver mating interfaces).  Yes, they get a bit dirtier running suppressed, but if you think you don't need to clean a suppressed piston gun basically just as much (depending on the suppressor, somewhat), that's simply not the case.  Without running a suppressor I don't feel the need to clean either more or less than the other either.

So, while I own some piston guns, it's mainly for the novelty of having something different because I can't realize any of their touted benefits to any appreciable degree in a civilian use case.  If you were going to drop me off in a war somewhere, the LWRC would without question handle shooting right after full submersion better than a DI gun due to the way the gas system on that particular rifle works, but outside of that I don't think I'd care.

I believe we're on the same page. You restated what I stated in the opposite order but from a consumer standpoint only. I was looking at both sides.
Pistons are manufacturer friendly. They're not necessarily consumer friendly from an inter-operability perspective.
The walled garden approach locks consumers into the builder's platform, its portfolio of IP protected replacement parts and even some accessories <cough HK>
That is in part why they like the idea versus rolling out another DI design.


My point exactly.


Yep.

I'd probably disagree on the that point with you. Gas buster charging handles and the like were not created because of GP guns. :)  Even running unsuppressed, the pistons tend to stay cleaner overall.

The benefits of the AR15's DI gas system (understanding that DI is somewhat of a misnomer) are essentially perfectly expressed in the overall AR15 design.

In short, there's not much benefit to using a DI gas system in a new design, that wouldn't be so close to an AR15 as to be pointless.

The AR15 also had a bad name for a very long time due to the myths/folklore/misconceptions about its gas system, so manufacturers in general had no interest in buying in to a system that already had a black eye to many consumers.

Interesting.

Any details / links?

I agree that, in general, pistons run cleaner both suppressed and unsuppressed.  My point was more that, as an example, if a suppressed DI AR can throw 3k rounds down the tube before failures due to fouling, is there a practical scenario where you're going to pop off 100+ 30rd pMags?  If not, it's a moot point unless you really don't like cleaning ARs.  In addition to that, you'd have to know the failure point for a piston AR due to fouling, if it's only 3.5k, you haven't gained much.

The other part to add to the mix is, not all piston ARs are of the same design.  PWS, for example, is long stroke with a tube leading back into the receiver that vents near the barrel nut.  LWRC is short stroke that vents near the gas block.  It's hard to draw a general conclusion for the totality of piston ARs with that in mind.  

I got rid of that POF308 (it was an older one) and picked up a 7.62 LaRue.  That POF wasn't even close to being in the same league.  A factory rifle should run from the factory, I shouldn't have to play around with recoil springs, polish the chamber, and such.  From the factory, the LaRue shoots softer, is better fit, and customer service doesn't suck.  A rifle that theoretically runs cleaner but doesn't run from the factory is hard to recommend.  The PWS works well on the lower/buffertube combination it's now on--zero problems.  The LWRC works on everything and, as I said previously, I would buy another based on my experience with it.  The only negative, which is specific to my LWRC, is that it doesn't have an adjustable gas block so I run a heavier spring for shooting suppressed which doesn't cycle lighter 223 loads with 100% reliability unsuppressed.  With the short stroke venting design, I could leave a lighter spring in there without any worry, I just choose not to beat it up unnecessarily since I mostly shoot suppressed.  

https://www.ar15.com/forums/t_3_121/207412_Lets-see-your-AR-10s.html&page=38

DUPE

pretty sure the LWRC IC-A5 has an adjustable gas bleeder. the IC-SPR does not.

the older M6A3's also had a 4 way adjuster, although i never noticed much difference between the suppressed and normal modes. i shoot that one on suppressed all the time with not ill effects.

Yeah, it's an IC-SPR.  Shoots a bit softer with the heavier spring, had it laying around, so why not use it?  Not a nock against the rifle at all, I wanted the longer handguard.

i have an IC SPR in the 14.7 pinned flavor. love the rifle and one of my most accurate barrels too.

i use the Vltor A5 buffer set up with an H3 or H4 buffer to keep it from beating up the rifle with its over gassed port. i wish LWRC would not to that, or any of the other mfg's for that matter.

i will say they cut a proper chamber though, mine will shoot that over pressure IMI m193 lot that is out there without any popped primers. can't say that about a few other barrels i own that are made by FN, BCM and BA.  althoughi have one BA barrel that will digest it.

sorry for the off topic minutia.

Ah.

Not the folder I was hoping for.
I was wondering if somebody came up with a viable way to ditch the buffer tube so it could be fired with the stock closed.

Neat rifle though.

ZM weapons made such a creature. cant recall who bought them though, maybe para ord?  i had one. it worked well but was nose heavy.

SIG... MCX, not DI though.

Someone already did; The Daewoo K1A1 series.

It uses two smaller diameter recoil springs with what essentially is a shortened carrier. Besides being longer though, the upper is taller inside.

That's it right there. There are not many ways to make a DI/bolt is a piston/carrier is a gas cylinder rifle.

ETA: Even the Daewoo K1 (the only other DI rifle I can think of since the AR10/AR15) is pretty much an AR15 with a different action spring.