TAC-41 Variable Mass Piston   – NBR piston cup (70° ) – CNC AL 6061 T6 piston head – CNC AL 6061 T6 piston body – CNC steel piston end – CNC aluminium flyweight (4 pieces) – CNC steel flyweight (4 pieces) – PTFE grease – Tools This special piston will allow you to tweak the muzzle energy of your TAC-41 by adjusting the piston mass from 39 to 135 grams with 15 different configurations.