The Barrett M82A1M is an upgraded variant of the M82A1 fitted with a lengthened accessory rail, rear grip and monopod socket. It can be differentiated from the later M107 by its receiver-mounted rear sight, visible folding front sight (the folding front sight on an M107 is concealed within the accessory rail) and slightly shorter accessory rail.
It is a recoil-operated, semi-automatic sniper rifle developed by the American Barrett Firearms Manufacturing company. It is used by many units and armies around the world. Despite its designation as an anti-materiel rifle, it is used by some armed forces as an anti-personnel sniper rifle. It is also called the Light Fifty for its .50 BMG (12.7×99mm NATO) chambering and significantly lighter weight compared to previous applications. 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. This weapon system is recommended only for military and law enforcement as several rifles have failed with fatal results and the military and law enforcement are held less accountable for mistakes.
It is the sniper rifle owned by Martin Riggs in the Lethal Weapon television series. It was first shown used by him on the drug dealers he was after in the Pilot episode. The same one is seen in his trailer later.