Gold & Silver Forum - What kind of round is this?

Quote:

MILITARY CARTRIDGE RELATIONSHIPS

� A G Williams

This is based on an article which first appeared in "Guns Review" magazine in April 1994, but has been much modified and extended.

It is taken for granted that whenever a new commercial rifle or pistol cartridge is introduced, it will probably be a derivative of an existing round. The 7x57 Mauser, .30-06 and .375 Holland & Holland Belted Rimless Magnum Nitro Express (to give it its formal title) have all parented huge families of variations in calibre, length or shape and are still doing so today. If a cartridge is genuinely new, such as the 10mm Auto, it is likely to find itself rapidly shortened (.40 S&W), lengthened (10mm Magnum) or otherwise molested in the interests of achieving some marginal advantage.

In contrast, military cartridges are rarely interfered with in this way. They are developed with little regard to cost for a specific purpose and once adopted remain unaltered for decades. However, there are well-known exceptions; the 7.92x57 was shortened to make the 7.92x33 Kurz cartridge for the WW2 German MP 43/44/StG 44 assault rifles, and the American .30-06 (7.62x63) was shortened to make the 7.62x51 NATO. Perhaps more surprising is that the 5.56mm NATO was developed from a commercial small-game cartridge - it's usually the other way round.

There have also been some heavy machine gun and cannon cartridges which were derivatives of existing service rounds and these are the subject of this article. Some of these are well known, others less so and some are quite surprising. The following groups of cartridges are illustrated by attached photos - just click on the links.

Group 1: Based on the .50" Browning.

This consists of the first five cartridges in this PHOTO, which are (from right to left): .50" Browning (12.7x99), 13.2mm Hotchkiss (13.2x96; also 13.2x99 and 13.2x93 are also found), .50.30 AP test (7.62x99), 10mm XM277 (10x107), .50 Spotter (12.7x76).

The .50" Browning was among the first of the heavy machine gun rounds, being introduced shortly after the First World War. During the interwar period a number of competitors emerged, of which the only survivor is the Soviet 12.7x108 round.

One which achieved considerable success at the time, being adopted by the French, Italian and Japanese (among others) was the 13.2mm Hotchkiss. The gas-operated gun was completely different from the recoil-operated Browning but the cartridge was remarkably similar in all dimensions except for calibre; in fact only an expert can distinguish them without having them side by side. The Italians designed the Breda M31 AFV gun around the cartridge. Even the Browning M2 aircraft HMG was chambered for this cartridge, by FN of Belgium and by the Japanese Navy Air Force, who called it the 13mm Type 3.

A more significant modification was made in Britain, which not only involved necking the case up to 13.9mm but also adding a belt, to create the .55" Boys anti-tank rifle cartridge (not shown in this photo).

The .50.30 looks remarkably similar to the German Patrone 318 (7.92x94) cartridge for the PzB anti-tank rifles, but it was only developed for testing AP bullets at high velocity.

The 10mm XM277 was developed in the 1960s for the GAU-6 rotary gun, apparently intended as a helicopter weapon. The cartridge reportedly generated a muzzle velocity of 4,000 fps (1,220 m/s). It might make the basis for a good long-range varmint rifle - if varmints ever grow to elk size! The gun was later modified to revert to .50 cal. Incidentally, it bears no relationship to the current GAU-19/A apart from the rotary configuration.

With the introduction of large-calibre recoilless anti-tank guns in the 1950s, it was decided that the simplest way of ensuring a hit with these low-velocity shells was to fit the gun with a ballistically matched spotting rifle firing bullets with a "flash" compound in the nose. The gunner fired the spotting rifle until a hit on the target was observed, at which point the heavy ordnance was triggered. There was much experimentation to develop the best cartridge for this purpose, but the most successful was achieved by simply shortening the .50" heavy machine gun round. Both large RCL cannon and spotting rifles are now obsolete; the former replaced by guided missiles, the latter by laser rangefinders. The .50" Browning soldiers on!

The same website had this to say:

http://www.quarry.nildram.co.uk/MCRel5.jpg

http://www.quarry.nildram.co.uk/MilRel.htm