The FN MAG (Mitrailleuse d'Appui General or General Purpose Machinegun), was designed by Fabrique Nationale around the 1950s. It is a gas operated, belt fed, air cooled automatic weapon. It uses the long piston stroke gas system with the gas regulator, located below the barrel. The bolt is locked using a swinging shoulder that engages the cut in the floor of the receiver. The air-cooled barrel is quick-detachable, with the carrying handle attached to it to help handling of the hot barrel. A regular belt for the FN MAG comes in a box of 220, and one in five rounds is a tracer. The receiver is made from steel stampings. The FN MAG is used by commonwealth countries such as the UK L7A2 and Canadian C6 GPMG, and adopted by the U.S. military as the M240 machine gun.