British .303 Browning Mk II* Aircraft Machine Gun

Britain began the process of replacing its Vickers aircraft machine guns with a new Colt/Browning design in 1935, with its adoption of the Colt MG40. This was essentially John Browning’s air cooled M1919 machine gun made smaller and lighter, with an increased rate of fire, and reversible feed direction. British adoption began with the purchase of 60 guns and a license for domestic production. This production took a few years to get rolling (by both the Vickers company and BSA), and in the meantime an addition 1600 examples were procured form Colt – including this example, dated 1937.

A few changes were made to the British pattern of the MG40. Most significantly, the clockwork was redesigned to run form an open bolt. This was deemed necessary because British cordite-loaded .303 ammunition was more sensitive to cookoff than American powders, and it would also detonate catastrophically upon cooking off. Unfortunately, this particular example has American ANM2 clockwork, so I can’t demonstrate that change here. In addition, the British developed their own muzzle devices. The initial pattern suffered badly from powder fouling, and the replacement pattern consisted of the booster seen on this example plus an option separate flash hider cone. It was primarily the changes in muzzle devices that prompted the change of designation from Browning Mk I to Mki*, MKII, and ultimate MkII*. In total, more than half a million of these guns were made during World War Two, forming the primarily armament for the RAF (including Spitfires, Hurricanes, and Lancasters).


  1. During their 1970s Bush War, the Rhodesian Air Force discovered their MAG58 and M2 .50cal machine guns couldn’t keep up with the speed of their Alouette helicopters when firing air to ground. Their solution was pairs of .303BR Brownings from other aircraft and through the kindness of allied countries. They tried mounting four Brownings but the rate of fire used up all the ammunition the helicopters could carry far too quickly. The other gun they found worked very well were 20mm French MATRA aircraft cannons.

    • The RhoAF did not use the M2 12.7mm HMG at all, the MAG GPMG (not MAG58 FN-H does not use that term) was extremely successful in that use. The .303in Browning used in pairs, were taken out of RhoAF stocks, they had been removed from the XXIV Spitfires used to the end of the 1950’s, two mounted in a pair in each wing, just transferred the whole across to the new mount in the helo. They tried the quad .303 in the G Cars (the command helo) for fire support, but the aircraft could not stand off to give effective firepower to the ground troops, and to control the ground/air action. The 20mm Hispano cannon was tried but, it produced too much kinetic energy for the cabin floor (they found a home in the Army with a ingenious ground mount). A very small number (?4) MATRA Cannon were obtained from Portugal in 1974, and found to fit the role perfectly, subsequently acquired from the RSA.
      SALT Beryl, with COOKE Wing Commander Peter, and SYKES Group Captain Bill. A Pride of Eagles The Definitive History of the Rhodesia Air Force 1920-1980. Covos Books, Johnaesburg, 2001. Hard cover, 1002p., photographs, drawings, maps, index. Gives a through description of this, and the tactical use of helo’s in Rhodesia, including the SAAF Puma’s used – they having the MAG GPMG fitted, the Alouette III’s used the MATRA (Alouette II’s were in use by both Air Forces).

      • The MAG 58 name refers back to the original Belgian nomenclature for that particular machine gun, and not necessarily the locally adopted name or number.

        From “Fire Force Helicopter Warfare in Rhodesia: 1962-1980” Dr J.R.T. Wood
        ‘To solve the problem of soft ground and trees, other guns were tried. Twin Browning .5-inch heavy machine-guns were fitted but were abandoned because of their weight and because the .5 bullet was not a cannon shell so a direct hit had to be scored to kill or wound, which could be achieved with the lighter .303 round.’

        The .50 cals were tried and evidently found unsatisfactory. That does not imply their continued use throughout the war.

  2. The reason for the cookoff problem is that the US used nitrocellulose (“gun cotton”) propellant and the Cordite is a mixture of nitrocellulose and nitrogylcerine so it burns “hotter” and produces more power per unit of weight. It’s also more dangerous and the US military has refused to use nitroglycerine in propellants to this day.

    “Abel, Sir James Dewar and W Kellner, who was also on the committee, developed and jointly patented (Nos 5,614 and 11,664 in the names of Abel and Dewar) in 1889 a new ballistite-like propellant consisting of 58% nitroglycerine, by weight, 37% guncotton (nitrocellulose) and 5% petroleum jelly. Using acetone as a solvent, it was extruded as spaghetti-like rods initially called “cord powder” or “the Committee’s modification of Ballistite”, but this was swiftly abbreviated to “Cordite”.

    Cordite began as a double-base propellant. In the 1930s triple-base was developed by including a substantial proportion of nitroguanidine. Triple-base propellant reduced the disadvantages of double-base propellant – its relatively high temperature and significant flash. Imperial Chemical Industries’s (ICI) World War 2 double-base AN formulation also had a much lower temperature, but it lacked the flash reduction properties of N and NQ triple-base propellants}”

    • “The reason for the cookoff problem is that the US used nitrocellulose (“gun cotton”) propellant and the Cordite is a mixture of nitrocellulose and nitrogylcerine so it burns “hotter” and produces more power per unit of weight. It’s also more dangerous and the US military has refused to use nitroglycerine in propellants to this day.”(C)

      Most countries switched to using double-base (with the addition of nitroglycerin) gunpowder back in the period between the great wars. Actually, when the reliable technology of its manufacture was finally worked out.
      Subsequently, most of the major manufacturers switched to tripple-base propellants. How more reliable and cheaper.

    • And regarding the explosion when overheated, the gunpowder is not to blame. Moreover, the gunpowder was almost the same, and the 30-06 did not do that.
      I think it’s about the construction of the brass. The bottom is too thin. If the gunpowder ignites from heating, and at this moment the primer is triggered by heating, it is quite possible to get detonation.
      Moreover, nitroglycerin and pyroxylin, both of them, are able to switch from combustion in a closed volume to detonation.

  3. “Clockwork” sounds to me like a spelling checker “at work”. I believe it was intended to be “lockwork”.

  4. Hurricane Armament Fit

    Hurricane I 8 X 303 Browning
    Hurricane IIA 8 X 303 Browning
    Hurricane IIB 12 X 303 Browning
    Hurricane IIC 4 X 20mm Hispano
    Hurricane IID 2 X 40mm Vickers S 2 X 303 Browning
    Hurricane IV 2 X 40mm Vickers S or 2 X 40mm Rolls Royce 2 X 303 Browning
    Hurricane X 8 X 303 Browning (Canadian Built)
    Hurricane XII 12 X 303 Browning (Canadian Built)
    Sea Hurricane IA and 1B 8 X 303 Browning
    Sea Hurricane IC 4 X 20mm Hispano
    Sea Hurricane IIC 4 X 20mm Hispano
    Sea Hurricane XII 12 X 303 Browning
    All Sea Hurricanes were conversions of RAF machines

    Spitfire and Seafire variations are extremely complex, for representative Spitfire and Seafire marks, see Supermarine Spitfire variants: specifications, performance and armament – Wikipedia

    For Spitfires & Seafires the suffix means

    A = 8 X 303 Browning
    B = 2 X 20mm Hispano 4 X 303 Browning
    C = 4 X 20mm Hispano (“universal wing”)
    D = Unarmed (Recon variants)
    E= 2 X 20mm Hispano 2 X 50 Browning

    Concise Guide To Spitfire Wing Types — Variants & Technology | Reference (

    • Note that RAF did early selected 20 mm Hispano Suiza as weapon of choice for their fighter, but due to various factors they used (a lot) x (rifle-caliber machine gun) as sort of stop-gap solution
      The Hispano (technically the Hispano-Suiza HS 404) was designed and developed at the French arm of the European Hispano-Suiza company in the mid 1930s. A firing demonstration of a prototype to British officers in Paris in 1935 banished all thought of the Oerlikon; the Hispano was similar in size and weight, slightly more powerful and fired nearly twice as fast. Unfortunately, the processes of obtaining approval to buy the gun, setting up a subsidiary Hispano factory at Grantham (the British Manufacturing And Research Company, or BMARCO), redrawing the gun to imperial rather than metric units, testing and debugging the prototypes, then fitting them into aircraft and debugging the installations, all took too long for the cannon to achieve anything in the Battle of Britain.

      • Strictly speaking, the Hispano and Oerlikon cannon were really different versions of the Berkigt cannon patents owned by the Swiss parent firm.

        Many parts, such as the barrels, were in fact interchangeable between the two.

        The principal player in all this was a clever salesman for Oerlikon-Buhrle named Antoine Gazda. He spent the years from 1934 to 1939 selling essentially the exact same cannon design (Hispano, Oerlikon, A Horse, a Spoon and a Basin or whatever he chose to call it at any given moment) to everybody from the Germans to the French to the British and ultimately the United States (Navy0. Each time convincing the customer that they were getting a top-secret design that absolutely nobody else had.

        And military ordnance development and procurement being the same then as now, everybody bought it, stamped it Top Secret, and went to work building it- and paying royalties to Oerlikon-Buhrle in Switzerland.

        The only ones who didn’t bite were the Russians. Because they preferred 23mm, and the Oerlikon/Hispano design wasn’t readily adaptable to their already-developed ammunition.

        When the war started, Luftwaffe planes began to fall in England, and RAF Recovery was telling Intelligence, “These German 20mm cannon look a lot like our”, Gazda and his bosses were back in Geneva, laughing all the way to the bank.


        Pawle, Gerald. The Secret War 1939-45. New York; HMCO, 1957. Chapter 6, “The Gun From Switzerland”.



        • While the Hispano was partially developed from the Oerlikon FF S, it was actually a gas operated locked breech cannon, while the original Oerlikons were all Advanced Primer Ignition (API) blowback weapons. Therefore they most definitely were NOT the same cannon, even if there were similarities. The German MG FF and FF/M were based on the lighter Oerlikon FF F and were also API blowback weapons. Again there was some family resemblance with the Hispano, but they were far from identical.

      • The. C wing more usually carried in each wing 1x 20mm Hispano cannon with 2 x.303 Browning’s.

        The SAAF used a few of the 4 X 20 mm armed ones in the Mediterranean and there’s a photo of an RAAF Mk VIII with the four cannon fit too.

        From the Mk.21 onward, the new shaped wing used 2 X 20mm Hispano per side. This was the same for the Mk.22 and 24

        Some Seafire XVs and XVIIs just had 1 X 20mm Hispano per wing.

    • The Beaverette looks like something a child might draw. Pretty peculiar project in general; quite a lot of work to put an obsolescent armament on a mobile platform. Obsolescent for AA use, that is. I suppose they had a surplus of those Bolton-Paul turrets. An interesting find from you as usual, thank you.

      • Perhaps obsolete for flak, but any idiot attempting to take out that car with rifle shot or concussion grenades would be reduced to hamburger.

    • The Beaverette was ad hoc vehicle quickly created in 1940 for Home Defence, subsequently used for training, Home Guard use, the RAF Regiment used both the standard and AA variants for air field defence. The quad barrel Boulton Paul turret (which was a very reliable turret) was very effective on such a vehicle ground mount (normally one round in three tracer), putting up 50 rounds per second. It was a very stable mount on the move, showing its ability during the Luftwaffe daylight raids on the UK Bomber Command airfields in 1943. Replaced with twin (or triple) 20mm Polsten Gun mounted on 4×4 15 hundredweight trucks. By the war’s end the same BP Turret with minor alterations was in use with two 20mm Hispano Guns on the new Lincoln Bombers (and the Lancasters fitted for Pacific operations with the USAAF) as mid-upper gun turrets.

  5. Very interesting once again Ian. Having known the AN-M2 .30 somewhat intimately, but not having worked with a .303 version I would be interested in a view of the internals of the Brit gun.
    They are really smaller versions of the .50 design than mods of the 1919.
    Side note: The US version(s) of the HS 404 are the AN-M1, M2, M3, and M24 (A1) some of which are still in use today, mostly as deck guns on patrol boats.

  6. Good info Stiven. Next time you have a 1917/1919 apart, compare the internals to the AN-M2 .30 and .50. The AN-M2 .30 is an absolute jewel of industrial art by the way. Curious as to why the Brit version has three mounting points, as the AN-M2 has two.

    • That is unlikely.
      I was played by both of them, but separately.
      I only paid attention to the conspicuous details (like the belt switch).
      In addition, the aircraft machine gun was from a downed plane and rather rusty, and then I did not know at all that the British were making them.
      It was a wing-mounted version with an early muzzle.
      The bolt carrier was lightweight, and the reciever was “all in holes” and all external elements are fixed with steel wire.
      And yet, it seemed to me noticeably lighter than the body of an ordinary M1917.

  7. Someone at Colt did not understand Roman numerals. This Mk II* is marked Mk11*. You’d think that, apart from sending us the wrong drawings, Colt would take the trouble to mark the bloody guns correctly!

  8. Did the British develop or licence-made any ground-use versions of this machine gun? With ground-use versions readily developed in production in the US, and with Britain able to produce 1,5 million of them during the war, it would have been an obvious consideration, to replace the old and heavy Vickers machine guns.

  9. The British produced .303 ammo with nitrocellulose grains (as compared to cordite) but the rounds were marked on the headstamp with the letter “Z” or as they say “Zed.” These were used in the ground role, but were made for aircraft use.

Leave a Reply

Your email address will not be published.