Guys, these are the finest piston driven uppers I have handled. I am a Range Officer at the Ben Avery Shooting Facility and Frank at POF USA does his testing out there. He's a really nice guy and lets us shoot all his neat toys. These are great on class III lowers. Nice consistent rate of fire and very clean. No gas rings and the receiver and bolt don't get near as hot as the conventional AR system, you can run this system dry with NO LUBE and it will run all day. If I could afford it, all my AR type rifles would have POF uppers. There is also a VERY noticeable reduction in recoil, especially under full auto fire.
Free plug for a nice upper.