In focus: the 50 cal heavy machine gun in Royal Navy service

In this article, Christopher Dwulet, author and editor for Ammo.com looks at the 50-calibre gun in use by the RN from the 50 Vickers and up to the 50 Browning Machine Gun still in use today.

There's something special about shooting a 50 calibre. The standard 7.62x51mm NATO is an excellent cartridge that has proven itself on the battlefield time and time again. But when you squeeze the trigger on a 50 cal, it's a completely different experience! Although 50 calibre heavy machine guns have been extensively employed by the Royal Marines and British Army for many years, recently the RN began re-evaluating the effectiveness of the 50 Browning for equipping its surface ships. (‘50 calibre’ refers to the diameter of the bullet which is .50 inches or 12.7 millimeters.)

The 50 Vickers or 0.5-inch Vickers was developed towards the latter part of World War I to meet the needs of the British Army. At the time a round that was effective against light armoured vehicles, planes, and tanks was needed. An anti-aircraft round was also an urgent requirement as Britain was being raided by the first generation of German bombers. These aircraft were able to absorb an absurd amount of .303 bullets from British interceptors without sustaining critical damage. The 50 Vickers was able to deliver the armour-piercing explosive or incendiary payload needed to down these aircraft quickly and efficiently.

The 0.5 Vickers was developed by Eley Brothers (Eley Limited today) by necking down the 600 Nitro Express to accept a 50-calibre bullet. The initial design utilised a rimmed case and fired a round-nose bullet. Further development of the cartridge case removed the rim and added a belt similar to the 375 H&H Magnum. The belted cases were headstamped ‘ELEY .600/500’, later versions of the case that were reinforced were labelled ‘ELEY .600/500A’. The new round was developed for use in a scaled-up version of the water-cooled Vickers and Lewis machine guns. The initial armour-piercing round fired a 570-grain bullet loaded with 135 grains of Dupont No.16 nitrocellulose resulting in a muzzle velocity of 2,650 feet per second (FPS).

The Royal Navy took note of the 50 Vickers’ anti-aircraft capabilities and adopted the platform in what became known as the Mark III. The Mark III was an anti-aircraft gun that consisted of four Vickers machine guns chambered for the 50 Vickers round. Each machine gun was loaded with a 200-round belt-fed magazine for a total of 800 rounds of 50 Vickers. The quad guns were adjusted to provide a cloud of plane-evaporating lead approximately 60 feet (18 m) wide and 50 feet (15 m) high at 1,000 yds (910 m). With a cyclic rate of 700 rounds per minute, the Mark III could completely unload its magazines in approximately 20 seconds.

Although the Mark III was very effective against biplanes of the WWI era, the Royal Navy quickly understood that the 50 Vickers simply didn't have enough firepower or speed to take down the new generation of faster and tougher aircraft. To combat this new threat, much of the fleet was outfitted with 20mm Oerlikon cannons or the heavier QF 2-pounder 40mm Autocannons (known more commonly as the ‘pom pom’). By the start of the second world war, the Mark III started to be phased out of naval service, except on coastal forces craft.

In 1921, American gun and cartridge maker John Moses Browning released his version of the 50-calibre cartridge. The 50 Browning Machine Gun (50 BMG) or 50 Browning was developed to fill many of the same roles as the 50 Vickers. (More about the development of the 50 Browning on Ammo.com here.)

Although comparisons between the 50 Vickers and 50 Browning were immediately made, until the second world war, the Admiralty seemed to favour the Vickers round over the 50 BMG. Trials were run in 1928 and 1934 comparing the two rounds, but in both cases, the 50 Vickers was selected over the American round. By comparison, the 50 BMG is the larger of the two rounds as the Browning measures 12.7×99 mm compared to the smaller 12.7×81 mm of the Vickers.

Although the RN was resistant to putting American weapons on British warships, the Blitz changed all that. In May 1941, President Roosevelt enacted the Lend-Lease Act whereby large quantities of military equipment were sold to Britain to hold the Axis powers at bay. It was then that the 50 Browning and its corresponding M2 heavy machine gun entered British military service. Although initial shipments of 50 Browning ammunition were made in the US, British manufacturers began production after 1941. Today Browning is owned by General Dynamics and the 50 Cal is still in production for forces around the world.

The L111A1 50 Cal used by UK forces is an automatic, belt-fed, recoil-operated, air-cooled, crew-served gun equipped with a flash suppressor and a spare barrel assembly. A disintegrating metallic link belt is used to feed the ammunition into the weapon which can be set up to feed from either the left or right side. The gun is capable of being modified to fire in single-shot mode but is predominantly used in automatic, firing 545 rounds per minute with a muzzle velocity of 930 m/s.

The 50 Browning or 12.7×99 mm NATO round has been used in combat since WWII. Its primary focus was as an anti-material cartridge, capable of blasting through brick walls, disabling vehicle engines, and lightly armoured targets. Early rounds were loaded with an 800-grain bullet fired at a muzzle velocity of 2,580 fps (786 m/s). Considerable development was performed on the 50 Browning round, and today numerous types of bullets are available for a multitude of military purposes.

Standard full metal jacket ammo is available for anti-personnel or unarmored targets, while armour piercing (AP) or armour piercing incendiary (API) rounds can be utilised on harder targets. For heavier targets that require a bit more power, military shooters prefer the Raufoss Mk 211 Mod 0 HEIAP (high explosive incendiary armour piercing) rounds for when you really want to get the job done.

Modern 50 Browning ammo is typically fired from a 1:15 twist-rate barrel with eight lands and grooves. It has been proof/test pressure listed at 450,000 kPa and can produce between 14,000 and 20,000 J of muzzle energy depending on the load. Given the heavy bullets fired by the 50 Cal, it is one of the few rifle cartridges that can boast a ballistic coefficient of 1.0. By comparison, the 7.62x51mm NATO has a G1 ballistic coefficient of around 0.40. Ballistic coefficient is a measure of how resistant a bullet is to wind deflection, and with a BC of 1.0 it is excellent for long-range shots beyond 1,000 meters.

Although the 50 Cal L111A1 Heavy Machine Gun has seen extensive use with the Royal Marines and British Army, the RN has generally preferred the lighter M134 Mk 44 Mini gun or L7A2 General Purpose Machine Gun (GPMG) for force protection.

The Fleet Air Arm has used the M3M 50-cal variant made by FN Herstal for some years when they are providing air cover or hunting down smugglers. The M3M can be fitted to Wildcat and Merlin helicopters and is adapted for aircraft use, featuring a firing mechanism that fires from the open bolt, internal recoil spring and a perforated barrel jacket. It has been considerably up-rated to fire up to 1,100 rounds per minute and a soft pintle mount and dual recoil buffer system reduces vibration transmitted to the airframe. Rounds are fed into the gun via a feeding chute that connects to a 600-round ammo box and spent cartridges are collected via another chute.

Despite its much greater hitting power than the GPMG or Mk 44, The 50 Cal benefits from being very reliable and robust, sufficiently light enough to be manhandled around the upper deck and easily mounted for use or removed for securing or for maintenance as needed. It can also be fitted with a variety of sights either simple iron sights, ring sights night vision or other optical sights above the spade triggers.

The 50 cal has now completely replaced the Mk44 mini gun which officially went out of RN service in March 2023, this is thanks to its longer effective range when compared to the 7.62x51mm rounds. This is driven in part by ever-evolving threats such as piracy and terrorist groups that favour smaller craft such as speed boats, jet skis, and RIBs for hit-and-run operations, The 50 Cal makes more sense as it allows sailors to engage potential threats at greater distances and can rip these craft apart at 2,000 meters even with simple ball ammunition.

When fixed to a standard pintle mount on a moving warship, the accuracy of the weapon is limited, especially beyond 1,000m. In November 2021 the NavyX and DSTL conducted a trial of a new Agile, Small-deflection, Precision (ASP) mounting on board HMS Argyll. The ASP mount is made in the US by Flex Force and uses gyroscopic stabilisation, increasing the accuracy and concentration of fire, especially in heavy seas. The trials team fired 5,000 rounds at static targets and a moving radio-controlled target boat. 3,500 rounds were fired using the new mounting for comparison with the old mount. At the time of writing it is unclear if the RN will invest in this upgrade for use across the fleet.