SRS Variable Mass Piston Weight Adjustable Silent Piston Each receiver has a unique

Each receiver has a unique engraved serial number

Next to that

SUS303 stainless steel's corrosion resistance is weakened due to its composition as it's specialized for machinability so the SUS304 steel we use is harder to machine but more durable and has wonderful corrosion resistance

This hop-up set comes with a high-quality stainless steel hop-up wheel with a clicker adjustment that prevents your hop-up from automatically rotating due to the MWS recoil

housed in a rugged and authentic stamped steel receiver set and CNC-machined trunnion

SRS Variable Mass Piston Weight Adjustable Silent Piston Each receiver has a uniqueSRS Variable Mass Piston NBR piston cup 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 For Pull Bolt Only This special piston will allow you to tweak the muzzle energy of your SRS by adjusting the piston mass from 40 to 137 grams with 15 different configurations.