Rugged's piston uses a non-slotted design creating a full circumference gas seal. This drastically lowers gas blowback for a more enjoyable shooting experience. Machined from 17-4 Stainless Steel and heat treated this piston is built to last. When using a piston on a fixed barrel platform such as a carbine or subgun the spring must be replaced with a Fixed Barrel Spacer. Features: Drastically lowers gas blowback 17-4 stainless steel construction Heat treated