It's a direct dimpingement gun. I am still whole heartedly in the "piston's are for suckers" when it comes to the AR platform. They are really looking for a problem for their solution. I'm well aware of the arguments, less heat, less dirt...blah blah blah. But seriously, do any of you think you'd shoot enough rounds between cleanings to justify the expense? The weight? Some systems are well thought out but most have not gotten past the added torque on the bolt carrier.
If you want a piston gun, buy one that was designed as a piston gun, not some retro-fitted abortion.