.50 Cal BMG Round

The .50 Browning Machine Gun round (.50 BMG) was developed at the end of the Great War by John Moses Browning to accompany his new scaled up machine gun. There was a need for a heavier machine gun to act as an anti-aircraft gun and the new cartridge was designed in the dying days of World War One to accompany this new scaled up Browning M1917 MG. The new machine gun did not arrive until 1921 so it would be the Second World War before it came into its own. The British were one of many nations that adopted the Browning .50 cal machine gun as an aircraft gun. British use of the .50 cal as an aircraft gun was limited as although more destructive than .303, by mid war the emphasis was on 20mm cannons which offered far more destruction than the upgrade to .50 offered. Today we are looking at a US manufactured, World War Two dated .50BMG round:

The round has a heavy 13mm diameter projectile which with a 290 grain loading has a velocity of around 900 m/s:

The round is rimless and has a deem extractor groove cut into the base of the cartridge:

This particular round is marked DM and has a date of 1943:

DM stands for Des Moines Ordnance Plant – Ankeny, Iowa.

Before the war  a number of weapons were evaluated for aircraft use, including .303″ machine guns (Vickers and Colt-Browning), .50″ weapons, and 20mm cannon. This involved both comparison of their statistics, and firing trials for performance, reliability, and effectiveness against aircraft targets.

The conclusion reached was that – for a given weight of armament, and allowing for fifteen seconds or so of firing time – eight .303″ Colt-Brownings could be carried by a single-engined monoplane, and would deliver some 160 rounds a second.

The .50″ Browning could, in the same weight, manage three guns, achieving 30–40 rounds a second; and while the larger weapon was more destructive, individual hits were not four times deadlier, while the larger number of .303″ bullets increased the chance of doing lethal damage.

The most effective weapon evaluated, the 20mm Hispano cannon, had a good muzzle velocity, high rate of fire, and used explosive shells with much greater effect on the target; but the desired armament of four cannon (to get enough rounds on target in a short exposure) was a much heavier installation, and the early Hispano was drum-fed and needed a very rigid mounting: it worked well in aircraft like the Westland Whirlwind, but needed development to go in a monoplane’s wings (the first effort to arm Spitfires with cannon failed badly).

So, the default fighter armament was 8 x .303″ guns, with intent to switch to 4 x 20mm cannon once aircraft could carry that weight. This pre-war approach shifted slightly with the Spitfire swapping four .303″ for two cannon; later in the war, the Spitfire’s ‘E’ wing carried two 20mm cannon and two .50″ Brownings, before the last versions went to four 20mm. Other fighters, like the Hawker Typhoon and Fairey Firefly, went directly to quadruple cannon and stayed there; there wasn’t an intermediate step of using .50″ weapons.

Combat experience generally suggested that the .50″ and similar weapons fell into an awkward niche: lacking explosive rounds, and with limited armour-piercing capability, they were quickly limited in utility against aircraft or tanks, with 20mm weapons largely replacing them. Meanwhile, they and their ammunition were heavy, meaning they really needed vehicles to carry and move them.

3 comments

  1. The cases make great bottle openers though 😉
    In API, the .50 was pretty good at Air-to-Ground, particularly against trains where piercing the boiler was enough to put an engine out of commission for a good length of time, 20mm did a better job but quite a few more .50 rounds could be carried for the same space and weight and sometimes “quantity has a quality all it’s own”
    It did a much better job against light armour than a .303 but for Air-to-Air you needed several and a good ammunition supply, something most US aircraft were designed for. The cartridge is still used today in the anti-materiel role and for long range sniping so it must be doing something right 😉

    • The other problem with use against aircraft was that towards the end of WW2 enemy aircraft were mostly proof against the .303 and the writing was on the wall for the .50 BMG as well. There was no answer to the 20mm Hispano (and for ground defence the 20mm Oerlikon and Polsten trailer-mounted quad). The German 20mm aircraft weapon used a short cartridge and had minimal penetration – Lancaster tail-gunners survived direct hits on the perspex canopy. (Everyone seemed to ignore the Hague convention that prohibited explosive ammunition under one inch diameter…)

  2. The Germans used 30mm in some of their A/C which was extremely effective although the muzzle velocity was low enough that aiming was a problem and it usually required them to get in close.
    A version of the Hurricane carried 40mm for anti-armour with mixed results and guns up to 75mm even appeared on some others, and a 105mm today on the various AC-130 gunships.
    The Luftwaffe started using unguided rockets as well, those were truly deadly and one hit was usually all it took on a B-17 but it was too little too late to make much difference in the war’s progress.
    Rockets would go on to be the main A-A armament from after the war until the mid-late 70’s when guided missiles finally became reliable enough to be the sole loadout and even then Rx were often carried as well and are still used today for A-G work.
    I wish I had a dollar for every one I built up or loaded.

    Funny thing about Rx, our 2.75″ ‘practice’ heads had a tungsten carbide rod inside for weight…
    When we started using our CRV-7 motors, they ended up punching holes in the Centurion and Sherman tanks we used for A-G targets and had to be switched for mild steel and even that did some pretty good damage. A 10 or 16 pound head doing 4,000+ fps leaves a dent that won’t buff out 😉

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