An automatic or semi-automatic rifle. The rifle has a receiver and a bolt having a striking surface, the bolt enclosed within the receiver. A barrel has a bore, the barrel coupled to the receiver. An indirect gas operating system has a cylinder and a piston, the indirect gas operating system mounted with a mounting structure substantially independent of the barrel. The cylinder is in communication with the bore, and the piston is fitted to the cylinder and disposed for striking the striking surface and displacing the bolt assembly.