The .50 Browning Machine Gun (.50 BMG) or 12.7×99mm NATO is a cartridge developed for the Browning .50 caliber machine gun in the late 1910s.
Entering service officially in 1921, the round is based on a greatly scaled-up .30-06 cartridge. it is a standard cartridge for NATO forces as well as many non-NATO countries. The cartridge itself has been made in many variants: multiple generations of regular ball, tracer, armor-piercing, incendiary, and saboted sub-caliber rounds. The rounds intended for machine guns are linked using metallic links.
The .50 BMG cartridge is also used in long-range target and sniper rifles, as well as other .50-caliber machine guns. A McMillan Tac-50.50 BMG sniper rifle was used by Canadian Army Corporal Rob Furlong of the PPCLI to achieve what was then the longest-range confirmed sniper kill in history, when he shot a Taliban combatant at 2,430 meters (2,657 yards) during the 2002 campaign in the Afghanistan War. (This was surpassed in 2009 by a British sniper in Afghanistan with 2,475 meters (2,707 yards) using a .338 Lapua Magnum (8.58×70 mm) rifle.)
A former record for a confirmed long-distance kill was set by U.S. Marine sniper Carlos Hathcock in 1967, at a distance of 2,090 metres (2,286 yd); Hathcock used the .50 BMG in an M2 Browning Machine Gun equipped with a telescopic sight. This weapon was used by other snipers, and eventually purpose-built sniper rifles were developed specifically for this round.
DARPA (Defense Advanced Research Projects Agency) has contracted with Lockheed Martin to develop the EXACTO program, including .50-caliber bullets complete with microprocessors and steering vanes that allow the bullet to adjust its trajectory mid-flight when the flight path has changed.
A wide variety of ammunition is available, and the availability of match grade ammunition has increased the usefulness of .50 caliber rifles by allowing more accurate fire than lower quality rounds. (WIKI)