ok piston if your shooting under 400FPS
I was pulling a m130 in an sr25 (uses same piston) and after about 200 shots in semi only (locked the gun to safe and semi-only operation) the piston split right down the middle causing the metal teeth to go up and into the piston disengaging them from the sector gear causing a grinding noise which also took off one of the 19 teeth on the gear..... Boy was I not happy when i found that...
good for 400FPS and under
compatible for sr-25 series
bad idea for 400+ FPS