.50 BMG
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The .50 Browning Machine Gun (12.7×99 mm NATO) or .50 BMG is a cartridge developed for the M2 machine gun and is now also used in long-range target and sniper rifles. The actual specified maximum diameter of an unfired .50 BMG bullet is .51 inches; while this appears to be over the .50 inch (12.7 mm) maximum allowed under the National Firearms Act, the barrel of a .50 BMG rifle is only .50 inches across the rifling lands, and slightly larger in the grooves. The oversized bullet is swaged to size upon firing, forming a tight seal and engaging the rifling. While subject to current political controversy due to the great power of the cartridge (it is the most powerful commonly available cartridge not considered a destructive device under the National Firearms Act) it is popular among long range shooters for its accuracy and external ballistics, and it is one of the few cartridges that delivers accuracy (if match grade ammunition is used) at ranges over 1000 yards (.9 km).
A wide variety of ammunition is available including ball, tracer, armor piercing, incendiary and saboted sub-caliber rounds. The availability of match grade ammunition has increased the usefulness of .50 caliber rifles by allowing more accurate fire than lower quality rounds. Matching the availability and price of the higher-quality .50 ammunition is an impediment to producing large caliber rifles using a different round such as 20 mm or another custom size.
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History
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. Image:50bmg.jpg 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. However, due to the incredible destructive power of the ammunition, such heavy-caliber sniper rifles are considered anti-materiel weapons.
.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.
Power
A common method for understanding the actual destructive power of a cartridge, is by comparison of muzzle energy. The Springfield .30-06 the standard caliber for American soldiers in World War II, (and a popular caliber amongst american hunters) can produce muzzle energies between 2000-3000 foot pounds. Where a .50 BMG can produce between 10,000 and 13,000 foot pounds or more depending on powder and bullet used.
Despite its tremendous power the .50 BMG cartridge is somewhat misunderstood. A current misconception is that the .50 rifles are capable of shooting down airliners, this is inaccurate. The M2 machine gun is capable of shooting down aircraft(many smaller caliber machineguns are also capable of being used in an anti-aircraft role), however; it fires at a rate of roughly 600 rpm making it possible for the operator to walk the tracers onto the aircraft, and make multiple hits. Due to their design and human limitations, a very skilled marksman with a .50 rifle is able to disable a parked aircraft.