Designed for use with the early Gas Trap version of the M1 Garand semi-automatic rifle, this device consists of three parts. The first part is a drop-in replacement for the standard muzzle device on the gas trap, marked "N.G." on the right side, threaded on the underside and with an internal bore diameter sufficient to pass a 30 caliber projectile. The next two parts are an unmarked oval collar that slides over the muzzle device, and a wide headed screw with compatible threading, serrations on the outer edge and a slot for a wide standard screwdriver. When fully assembled the screw head chokes down the diameter of the muzzle device's bore by over a third. In operation this would obstruct the escaping gas from a blank cartridge permitting a proper buildup of pressure in the gas trap to cycle the arm.