Browning 0.50 M2 Machine Gun

This article deals with the Browning primarily as an aircraft and naval weapon. See the article on Small Arms for further discussion of the Browning as an infantry weapon.

U.S. Army

Specifications:

The Browning 0.50 machine gun was a successful heavy machine gun design when used on land and in the air.  It traded a relatively low rate of fire for range, accuracy, and hitting power, having a significant armor piercing capability against aircraft armor and light Japanese tanks.  

The M2 had a long lineage, being developed in 1933 from the M1921 0.50 caliber Browning machine gun, which was itself developed from the M1917 0.30 caliber Browning machine gun. It had become evident during the brief American intervention in the First World War that the 0.30 bullet did not have adequate penetrating power against the armored vehicles and aircraft that were beginning to appear on the battlefield. The Americans were impressed with the French 11mm (0.43") armor piercing incendiary bullet, but an attempt to rechamber the 0.30 machine gun to take the 11mm cartridge was not particularly successful. Pershing demanded a bullet weighing not less that 670 grains (1.53 ounce or 43 grams) with a muzzle velocity of at least 2700 fps (820 m/s). John Moses Browning began work on a scaled-up version of the M1917 while Winchester developed a scaled up 0.30-06 cartridge. Pershing again intervened to demand that this be a rimless cartridge (Winchester originally envisioned a rimmed cartridge that would also be suitable for an antitank rifle) and the prototype was first test fired on 15 October 1918. Like the 0.30 Browning, the 0.50 Browning used a closed short recoil action. It differed from the 0.30 Browning chiefly in using an oil buffer to more effectively absorb recoil. This buffer could also be adjusted to alter the rate of fire. The gun was found to have a rather low maximum rate of fire and it did not reach the 2700 fps muzzle velocity requirement, but plans were made to manufacture 10,000 units with a longer barrel that was projected to achieve the required velocity. However, the gun was heavy (160 lbs or 73 kg), clumsy, almost impossible to fire accurately, and lacked the necessary armor penetration. Further work at the Frankford Arsenal turned the M1921 into a serviceable fixed antiaircraft weapon, but it was never much of a success as an infantry weapon.

Beginning in 1932, Colt worked with Springfield Armory to developed a revised version of the M1921, which eventually became the M2 Browning. The Army lacked the funds to support development but persuaded the Navy to take an interest in the new design, and the first orders were placed in 1933. The M2 was further revised in 1940 with a lighter barrel and double recoil springs that improved its nominal rate of fire. Reliability steadily improved throughout the war, reaching a low of one jam per every 4000 rounds fired. The M2 eventually became a family of closely related 0.50 caliber machine guns using the same receiver but different barrels, cooling systems, sights, or back plates. These included the Browning Machine Gun, Caliber 0.50, M2, Water-Cooled, Flexible; the Browning Machine Gun, Caliber 0.50, Aircraft, AN/M2 Fixed or Flexible (the AN standing for "Army-Navy"); and the Browning Machine Gun, Heavy Barrel, Caliber 0.50, M2 HB Fixed, Flexible, or Turret.  The M3 was developed at the very end of the war and achieved a rate of fire of 1200 rounds per minute, a new record for a heavy machine gun. All versions were fed with disintegrating metal link belts of 110 rounds each, and the belts could be fed from either the left or right side by changing a few parts. This could be done in the field in a matter of minutes. The water-cooled ground version could apparently use a fabric belt as well as a disintegrating metal link belt.

Both air-cooled and water-cooled versions were used in ground combat. The air-cooled ground combat version, the M2 HB, used a thicker barrel to allow it to stand up better to the heat from firing. The AN/M2 aircraft version used a light barrel in spite of being air-cooled, since the slip stream provided a flow of cold air that efficiently cooled the gun. In fact, the aerial version of the gun often came with an electric heater that could be clipped onto the receiver to keep the action from freezing at high altitude.

Both the ball and AP rounds consisted of a steel core in a brass jacket with a lead alloy point filler. The soft jacket and point filler acted much like the cap on a large-caliber APC round, improving penetration. The AP round differed from the ball round in using a very hard (and expensive) tungsten chrome steel core.  The AP round had a nominal penetration of 0.83" (21 mm) at normal impact at a range of 600 feet (183m). However, this dropped rapidly for oblique hits or if the bullet was subject to yaw. The typical penetration during air combat was 0.39"-0.59" (10-15 mm), which was normally still adequate.

Barrel wear was a significant problem for the aircraft version of the weapon, and aircrew were trained to fire no more than a 75 round initial burst and 25 round bursts thereafter. A longer burst would overheat the barrel, wear out the rifling, and destroy the accuracy of the gun. In January 1944, the U.S. Air Force adopted chromium alloy (Stellite) barrel liners that reduced wear and allowed much  longer bursts.

The Browning was much less successful as a naval antiaircraft gun than in ground or air combat, and it was replaced with 20mm Oerlikons as fast as these became available.  The 0.50 round was simply not heavy enough to do the job.  The weapon was more effective in its role as an antipersonnel weapon on submarines, PT boats, and other small craft.

Photo Gallery

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Video of a modern 0.50 Browning being fired in training

References

Campbell (1985)

Chin (1951; accessed 2013-11-30)

Hogg (2001)

OPNAVE 33-40 (1944; accessed 2012-11-28)
Williams and Gustin (2003)

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