Quote History Quoted:
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.
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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.