Expanding powder gases furnish the energy for the operation of the gun. After the gun is fired and the bullet has passed the gas port in the barrel, the live powder gases expand through the gas port into the gas cylinder and impinge against the head of the piston. This sudden blow forces the piston to the rear, compressing the recoil spring and storing up energy for the return movement. The various lugs and cams actuate the feeding, firing, extraction and ejection, and also control the operation of the gun. The feeding is accomplished through a magazine holding 20 or 40 rounds in double rows. It is held between the sides of the receiver, in front of the trigger guard. This magazine is composed of a rectangular tube and a round wire spring wound to fit the tube. Also there is a bottom plate which slide in the bottom and forms the rest for the spring. On top of the spring is a follower, which forces the cartridge up against the lips of the magazine tube and which holds it in place until stripped out by the lug on the bottom of the bolt. The automatic action of this gun is not disturbed by holding it in any position whatever. The magazine can be inserted while the mechanism of the gun is in either the cocked or forward position. All parts of the gun are designed so as to impose a minimum of shock and strain upon them. They are also made strong enough to hold up under the maximum amount of work that they can be made to perform. There are few parts that can be assembled incorrectly but the gun will not function unless these parts are assembled correctly. The dismounting and assembling of the rifle can be accomplished without the aid of a single tool unless the barrel and gas cylinder are removed which necessitates the use of a special spanner wrench provided in the kit. General Data. Weight of gun 15 lbs. 8 oz. Weight of Magazine, empty (20 rounds) 7 oz. Weight of Magazine, filled (20 rounds) 1 lb. 7 oz. Length of barrel 24 inches. Sights graduated up to 1,600 yards. Calibre bore 0.30 inch. Gas port form muzzle 6 inches. Rate of fire 500 shots p’m. Aimed shots per minute, semi-automatic 60 shots p’m. Weight of bullet 150 grains. Weight of Powder 47 grains. Weight of Cartridge (total) 395.5 grains. Chamber pressure, pounds per square inch 47,000 to 50,000. Muzzle velocity 2,682 ft. p’s. Habitual type of fire semi-automatic. Cooling System.