The Modify Tremors Recoil Action Kit is a revolutionary recoil system made specifically for the M4 AEG. This kit uses the power of the piston to transfer energy into the buffer tube of the M4 carbine, the result is a realistic recoil feeling with every shot. Other blowback systems only simulate the movement of the bolt, but this tremors kit actually create recoil and puts it into your shoulder! The kit includes 8 pieces and requires the opening of the gearbox, so professional installation is recommended. This is yet another way to add amazing realism to your airsoft gun.