Developed in the early 1900's, the .50 BMG still sees wide use to this day. John Moses Browning developed the cartridge by scaling up the .30-06 cartridge to a much bigger size. It has been fired from vehicle-mounted weapons, including WWII fighter aircraft, and is still being used today on helicopters and ground vehicles. The cartridge is also fired from sniper rifles. The cartridge is hardly ever used for hunting, but it would easily kill any living creature on earth.
The standard load for the military fires a full metal jacket bullet weighing 647 grains and travelling just more than 3,000 feet per second. Heavier bullets weighing 800 grains and moving 2,900 feet per second have also been used. These numbers are reached in the M2 heavy machine gun with a barrel 45 inches long. Many sniper rifles barrels are shorter, so the muzzle velocities are correspondingly lower.
The M2HB machine gun is the most famous weapon chambered for .50 BMG, but it is also chambered in the M3 machine gun, and the Barrett M82/M107 family of sniper rifles, the MacMillan TAC-50, and many other precision and anti-material rifles.