History of the 50 BMG cartridge
The usefulness of an anti-armor weapon usable by infantry was proven by the Germans during World War I, where they developed the 13mm TuF, which proved capable of severely damaging the new British tanks. After seeing the benefits of such a weapon, the United States developed the .50 BMG to serve a similar role.
During World War II it found its usage in penetrating lightly armoured vehicles, including aircraft. An upgraded variant of the Browning machine gun used during World War 2 is still in use today as the well known M2 machine gun. Since the mid-1950s, armoured personnel carriers and utility vehicles have been made to withstand 12.7 mm machine gun fire, thus making it a much less flexible weapon. It still has more penetrating power than light machine guns such as general purpose machine guns, but is difficult to maintain and aim in field conditions. Its range and accuracy, however, are superior to light machine guns when fixed and water cooled, and has not been replaced as the standard caliber for western vehicle mounted machine guns (Soviet and CIS armoured vehicles mount 12.7 mm DShK, NSV, which are ballistically very simiar to the .50 BMG, or 14.5 mm KPV machine guns, which have significantly superior armour penetration compared to any 12.7 mm round).
The Barret M82 .50 Caliber rifle and later variants were born during the 1980s and have upgraded the anti-material power of the military sniper. A skilled sniper can effectively neutralize an infantry unit by picking off several soldiers at a very long range, without revealing his precise location, then spend a few hours moving to a new position (whether they decide to hunt down the sniper or to retreat), before firing again.
A Canadian sniper in Afghanistan used a .50 BMG rifle to kill a Taliban guerilla at 1.5 miles (2,430 m) during Operation Anaconda.
.50 ammunition has even been used in some curiosity handguns such as the Maadi-Griffin handgun and Thunder 50 handgun. They have much shorter barrels than rifles firing the round, so do not have the same muzzle velocity. The .50 BMG round is loaded with a large-grain ball rifle powder which requires a rifle-length barrel for a complete burn and so even aside from recoil and size considerations, the round would perform relatively poorly in ballistic terms, and with an immense flash from propellant being uselessly burned outside the bore, in a true handgun-length barrel.
The round was used as a basis for developing that of the Boys anti-tank rifle, which used a belted design and a slightly larger-diameter bullet.
It should be noted that the US military has profited a great deal from civilian use and refinement of this venerable cartridge, and that without the civilian interest our convential forces would be well behind the 'power curve' that they dominate to this day.