BARRETT M82 (U.S.A.) -The M82, standardized by the US Military as the M107, is a recoil-operated, semi-automatic anti-materiel rifle developed by the American Barrett Firearms Manufacturing company. Designated as a heavy SASR (Special Application Scoped Rifle), it is used by many units and armies around the world. It is also called the “Light Fifty” for its .50 BMG (12.7×99mm NATO) chambering. The weapon is found in two variants, the original M82A1 (and A3) and the bullpup M82A2. The M82A2 is no longer manufactured, though the XM500 can be seen as its successor. The M82 is a short recoil semi-automatic firearm. When the gun is fired, the barrel initially recoils for a short distance, before being securely locked by the rotating bolt. After the short travel, a post on the bolt engaged in the curved cam track in the receiver turns the bolt to unlock it from the barrel. As soon as the bolt unlocks, the accelerator arm strikes it back, transferring part of the recoil energy of the barrel to the bolt to achieve reliable cycling. Then the barrel is stopped and the bolt continues back, to extract and eject a spent case. On its return stroke, the bolt strips the fresh cartridge from the box magazine and feeds it into the chamber and finally locks itself to the barrel. The striker is also cocked on the return stroke of the bolt.
