btw watch out for
Defective product alerts: Guarder polycarb piston head
http://www.airsoftcanada.com/showthread.php?t=30528
"
POLYCARB PISTON HEADS
http://www.intrudershop.com.tw/mmc/i...E-04-03_01.jpg
Nice looking ventilated piston head with a machined brass insert for the screw to tap into. However polycarbonate has not shown itself to be sufficiently fatigue resistant for the repetitive hammering in a mechbox.
Colin_S has broken two piston heads in his M14 and P90. I have found that the piston material is not very impact resistant in tests at the shop."
but the thing is many maufactuers make polycarb piston heads sucessfully so I ended up with a polycarb head anyhow.
If it breaks, it breaks.