History:

Using a round originally designed by Winchester, the .50 BMG round was designed as a response to the German 13 mm anti-tank rifle of World War I and employed in a redesigned and scaled-up M1917 Browning .30 cal. machine gun. It was quickly adapted to the anti-aircraft role. It was also selected for the ground role and adopted by the U.S. as the Model 1921. The latter served during the 1920s as an anti-aircraft and anti-armor gun. In 1932, the design was updated and adopted as the M2, though fulfilling the same role. As with the M1921, the original infantry variant of the M2 was equipped with a water jacket for cooling.

A variant without a water jacket, but with a thicker-walled, air-cooled barrel superseded it (air-cooled barrels had already been used on variants for use on aircraft, but these quickly overheated in ground use). This new variant was then designated the M2 HB (HB for Heavy Barrel). The added mass and surface area of the new barrel compensated, somewhat, for the loss of water-cooling, while reducing bulk and weight (the M2 weighed 121 lb (55 kg), with water, whereas the M2 HB weighs 84 lb). Due to the long procedure for changing the barrel, an improved system was developed called QCB (quick change barrel). A lightweight version, weighing 24 lb (11 kg) less—a mere 60 lb (27 kg)—was also developed. The Army is looking for a light weight replacement for the M2 as of 2008.

Work In Progress