THE HEAVY MACHINE GUN CARTRIDGE PART 3: EXPERIMENTAL ROUNDS UP TO 1945

By Anthony G. Williams

.500 Colt Kynoch (.50 North)

This cartridge was developed in 1901 in the UK in at least two versions, including rimless, but the semi-rimmed is the most common. Only a few brief notes concerning the ammunition have survived, and nothing is known about the gun except that it was presumably a scaled-up version of the Colt MG. The term “.50 North” is sometimes used; a Mr T.K. North was based in London as a senior employee of the Colt company at that time. Considering its age and obscurity, the cartridge is surprisingly common in collections.

.500 Colt Kings Norton

Also known as the “Colt .500 Long Range Experimental”, this rimmed cartridge was developed by the Kings Norton ammunition factory in the UK in 1912. Again, there are just a few surviving notes about this round, of which only one specimen has been found. It was presumably designed with a Colt machine gun in mind.

13mm TuF

This is of course the “Father” of all modern HMGs which inspired the development of the breed. It was devised during the Great War for the dual purpose of dealing with tanks and aircraft – hence the designation, TuF standing for “Tank und Flieger”. The gun was a scaled-up Maxim. It took some time to develop, so Mauser produced a big bolt-action rifle – the M1918 T-Gewehr – chambered for the same 13x92SR ammunition. This did see action, and is probably responsible for the fact that the ammunition is still easy to find (many soldiers must have picked up thebig rounds as souvenirs). By the end of the war, some 24 examples of the TuF were known to have been completed by Maschinen-Fabrik Augsburg-Nurnberg and distributed in batches of three to eight different army units but these did not, it seems, arrive in time to see any action.

There is one amusing side-note to the story; some sources claim that the “Tank und Flieger” refer to what the gun was meant to be fitted to rather than to its targets, despite the fact that it was only ever made as a water-cooled gun on a wheeled artillery mounting, and in that form wasfar too big and heavy to have made a practical aircraft gun. There is a letter in the British National Archives, dated March 1921, which may explain where this misperception came from. The British were making efforts to acquire an example of this gun, but the Military Committee of Versailles had previously decided that the TuF was an army weapon, and therefore not subject to seizure under the terms banning aircraft armament. So the British tried to argue that the gun could easily be adapted for use in aircraft, so it ought to be considered as an aircraft weapon! It appears that this ingenious ploy was unsuccessful.

.55 Boys

It may seem odd to include a service anti-tank rifle round in an article about experimental HMG cartridges, but one Rolls- Royce MG was designed around the .55 inch. There was in fact a series of R-R aircraft guns, some recoil-operated (Type AA) and some gas-operated (Type AB), initially in 13.2×99 Hotchkiss and later in 12.7×99 (.50 BMG). There was a plan to adapt the gas-operated design to the .55 Boys ammunition under the designation Type CB. All three of these cartridges were of course dimensionally very similar, differing only in calibre and (in the case of the Boys) the addition of a belt, so switching calibres was straightforward. However, in October 1941, before the conversion to .55 could be carried out, Rolls- Royce was instructed to stop messing about with guns and focus on aircraft engines.

Some reports claim that the Italians designed an MG around captured stocks of the .55 Boys cartridge, but apart from being inherently improbable (it had no significant advantage over the 13.2×99 Hotchkiss they already had in service) drawings have been found of a separate Breda cartridge of the same calibre.

.661 Vickers

This is probably the biggest HMG cartridge ever made. It resulted from a mid- 1930s Royal Navy requirement for a new light AA weapon to replace the .5 inch Vickers; more range and hitting power were asked for. Vickers duly produced this massive cartridge and one multiple-barrel mounting to fire it, although no details of the gun are available. It was cancelled in 1939 in favour of acquiring the 20mm Oerlikon Type S, which had less impressive ballistics but did fire the explosive shells which the RN had decided were essential to produce adequate terminal effects. The .661 cartridge was briefly revived in 1942 for some high-velocity penetration tests against armour plate. Chambered in a pressure barrel, it fired light (660-710 grain) bullets at up to 4,500 fps, but the results were disappointing. The cartridge is now a rare item, existing in only a few collections (not, unfortunately, including the author’s).

.60 Cal

This was the only American HMG cartridge to pose a serious threat to the dominance of the .50 BMG. It originated in a requirement for an anti-tank rifle, which duly emerged as a massive semi-automatic, gas-operated, strip-fed, tripod-mountedweapon. Only one gun was made, by the Springfield Armory, and this was tested at the Aberdeen Proving Grounds in October 1942 and again in June 1944, but no orders were placed. However, the very powerful ammunition attracted the attention of the USAAF, who at that time rated a high muzzle velocity as being of overriding importance in an aircraft weapon because of its benefit in increasing the hit probability. (It is worth noting that every other major air force disagreed with them, preferring to trade some velocity to obtain the greater destructive power of 20mm or larger cannon shells, but exploring that issue is beyond the scope of this article.)

Two existing guns were modified to fire the .60 cal. ammunition. One was the 20mm Hispano, designated in modified form the .60 T18, the other was the German Mauser MG 151, which became the .60 T17. The T17 proved the most satisfactory and about 300 guns were made; adoption by the USAAF was a distinct possibility. But compared with the .50 M2 the gun was heavier and slower-firing, and it seems that its advantages were not felt to be sufficient to be worth the trouble of replacing the big Browning.

The .60 cartridge remained in the running for new aircraft guns even after theend of the war. The new US revolver gun, based on the Mauser MG 213C, was initially made in this calibre as the T130 (it would have been designated the M38 had it entered service). The first prototype of the Vulcan rotary gun, the T45, was also made in .60 calibre. However, the USAF ultimately decided that such big guns should fire more effective ammunition, so the .60 cartridge case was necked out to 20mm calibre and shortened to keep the overall cartridge length the same, creating the famous 20×102 round still in front-line service today. The revolver gun in this calibre became the M39, and the six-barrel rotary the M61. The .60 cal. cartridge therefore never saw service, but it is still a common collectors’ item.

.50/60

As the designation suggests, this was simply a .60 cal. case necked-down to take a .50 calibre bullet. This 1944 project was the ultimate expression of the USAAF’s World War 2 obsession with high muzzle velocity and certainly set the record in this respect, achieving no less than 4,400 fps with the light T49 API bullet. However, judging by the relative rarity of this round, it was not given very serious consideration.

.50 HV (High Velocity)

The result of yet another Second World War attempt by the USAAF to achieve a very high-velocity machine gun, this was simply the 20mm Hispano case necked down to .50 calibre, and fired in a modified Hispano cannon. Work started in 1942, but it was dropped as a contender in 1943, following a decision that the .60 cal. showed more promise. However, the round was retained in use for high-velocity bullet test purposes up to 1945.

13mm and 15mm MG 215

The German armament industry was highly prolific during the Second World War, and particularly so in the case of aircraft guns. Many different types saw service, and many more were developed but not adopted. One of the latter was the Mauser MG 215, made in two new calibres – 13x92B and 15x83B. These were compact, gas-operated weapons, intended to replace the little 13mm MG 131 but offering much higher performance. However, they did not emerge until 1944, by which time the Luftwaffe had other priorities – namely, large-calibre cannon for attacking heavy bombers – and only a few specimens were made before they were rejected.

Other experimental HMG cartridges

This is very far from a complete listing of the experimental HMG rounds made up to 1945, just some of the more significant or interesting ones. Some only remained as paper projects, and the second photograph with this article illustrates some modern replicas of these more obscure rounds.