An improved gas piston system for the automatic loading of a rifle, especially a rifle of the M-16/AR-15 type. The system employs a barrel nut, or an adaptor to a barrel nut, that has been modified to secure one end of a gas piston system. The other end of the gas piston system, namely the piston rod, engages, either directly or indirectly, the key on a bolt carrier group. This configuration positions the gas piston system at a point starting near the barrel nut and extending to the bolt carrier group of the rifle, while a gas tube extends from the gas block to the gas piston system a point near the barrel nut.