CUSTOM SHOP BUILD FOR AUSTRALIA SEMI AUTO CATEGORY D RIFLE 30 SHOT, 16" BARREL PISTON DRIVEN GAS SYSTEM 1 IN 8" TWIST, 16" BARREL With only one moving assembly, the PWS long-stroke piston system offers a lighter recoil impulse, while at the same time providing increased longevity and durability. A floating piston head, detachable for charging handle replacement, is attached directly to the operating rod, which in turn is securely attached to the carrier. Our four position adjustable gas block restricts gasses, rather than venting them from the side. This allows the unused gas to exit from the front of the gun, rather than the sides of the gas block, resulting in a more quiet operation.