"Stripped original piston in my ksp90 with a modified prometius 135(400 to 440 fps) spring. Have had no problems from this piston n head. .25 gram bbs fly accurate and FAR. PENETRATES 5 PLUS LAYERS CORRUGATED CARD BOARD AT 6 INCHES. AWESOME. Oh had to remove reverse latch because if stopped in back position, motor cannot overcome spring. ROF slower 10 per sec. but way more power and performance. P.S. piston head fits cyl precisely. Unlike original. 1600 shots so far. No problems"