Look back in the archives, Mrraley had some good discussions,on,piston rifles. A key is the AR was not designed from the start to be a piston weapon. So any manufacturer adding one needs to do their homework about effect on balance, reliability, durability, ammo compatibility and a host of other factors. And that is just to prove equivalence to direct impingement AR’s. To prove superiority they would have to do tests of 10’s of 1000’s of rounds, and have a significant difference. An argument can be made whether a piston driven rifle is even still an AR .