After running 300 Rounds thru, & a lot of fiddling, got this thing working like it should. 1st-Balance. With 2 loaded mags. in the stock, it is way too stock heavy for accurate, quick sighting. I added some barrel weights at the end of the barrel, to get it to balance, got the result, then added an old compensator, of the same appox. weight. Then the Optic. Mounting an optic at the end of the rail, exceeds the eye box of most optics. It's usable, but very difficult. I added an aftermarket Optic mount that moves the optic back, into the eye box zone. What a difference!Now this FPC operates as it should.........