WARNING -- this article is a minefield of technical anoraky
To the layman and journalists (who are, after all, lower than laymen), a 7.62 mm is a bullet. Used by, like, soldiers in their, like, guns. It fits in a AK-47 and a MAS 49, and an SLR and a Dragunov and Gucci SR 25, all of which you learnt by playing "Counterstrike" and "Rainbow Six". It's really, like, big and powerful, and being hit by one will send you flying through the air through a plate glass window and the recoil is so big you have to have special training so says Nobby down the pub and he was the first guide through the window at the Iranian Embassy siege so he knows, okay? Whatever.
7.62 mm ammunition comes in a variety of flavours, listed here by cartridge length.
- 7.62 x 25 mm -- also known as 7.62 mm Tokarev. This is a bottlenecked rimless pistol cartridge adopted by the USSR in 1930 with the Tokarev TT-30 automatic pistol. This cartridge is essentially an unabashed copy of the old 7.63 x 25 mm Mauser cartridge of "Broomhandle" fame and 1890s design, but is a little spicier.
- 7.62 x 33 mm-- not to be confused with the 7.92 x 33 mm Kurz. This intermediate round is more of a pistol round and was used in the M1 Carbine.
- 7.62 x 38R -- also known as 7.62 mm Nagant revolver . This is a bizarre and anaemic revolver cartridge with the bullet completely enclosed inside the case. the reason for this is that the M1895 Nagant revolver had a cylinder which moved forward on cocking such that the case mouth sealed the flash gap off.
- 7.62 x 39 mm -- the famed Kalashnikov cartridge. A true intermediate cartridge, with ballistics between those of pistol cartridges and "proper" rifle cartridges. Bullet diameter is .311 inch.
- 7.62 x 45 mm -- a short lived Czech intermediate cartridge which was rapidly superseded by 7.62 x 39 mm with the absorption of Czechoslovakia into the Soviet bloc.
- 7.62 x 51 mm -- the infamous 7.62 mm NATO. This cartridge is essentially a .30 M2 (see below) with a shorter case length and similar/identical ballistics. Britain wanted to bring in an excellent .280 inch intermediate cartridge, but the Americans refuse to countenance the adoption of anything with ballistics inferior to that of .30 M2. Advances in powder technology over the previous 40 or 50 years meant that the same ballistics could be achieved in a shorter case, and thus 7.62 mm T65 was born and was adopted as the 7.62 mm NATO cartridge. .308 inch Bullet diameter.
- 7.62 x 54R -- this cartridge has the distinction of being the longest serving cartridge in military use today. It was adopted by Russia in 1891 for the M1891 Nagant rifle, gained a pointed spitser bullet in 1908, and is still in service today with the Dragunov rifle and the PK series of machine guns. The cartridge was adopted with a rim because that allows much larger chamber tolerances, and Russia was hardly an industrially competent power at the time of its adoption. It was never replaced largely because it was there and it worked. Bullet diameter is .311 inch (actually the same as British .303 inch), although nominal diameters can range from .310 to .313.
- 7.62 x 63 mm -- better known as .30-06. This, in three main flavours, was the standard American rifle cartridge for around 50 years. Its original form, officially called .30-06, proved to be a poor performer at long range (as in high angle machine-gun barrages) in the First World War, so it was briefly superseded by .30M1 in the post-war period. Whilst being an infinitely superior cartridge, the .30 M1 had a higher felt recoil and outshot the range templates on practice ranges, so was almost immediately replaced by a "training" cartridge which replicated the original ballistics and was named .30 M2. Due to the lower felt recoil, the .30 M2 was preferred to the .30 M1 cartridge, and was standardised. By this time, there were none of the British trained Doughboys left around who had cut their teeth on long-range Vickers barrages to complain about the awful long-range ballistics. Bullet diameter is .308 inch.