.303 Mk VII
.303 Mk VII was the standard .303 round used in the Lee Enfield service rifle, Vickers Machine Gun and Bren Light Machine Gun. The number of distinct .303 rounds, including different manufacturers and details of ammunition, run in the hundreds if not thousands; many collectors dedicate themselves solely to .303 variants, and no complete collection (i.e. with a single sample of every known variant .303 round) is known to exist.
The .303 is known commercially today as either .303 British or 7.7 x 56R. This cartridge was first developed in Britain in the 1880s as a black powder round and later adapted to use cordite and then smokeless powder propellant. It was the standard British and Commonwealth cartridge from 1889 until the 1950s, when it was replaced by the 7.62mm NATO round.
The Cartridge, Small Arms, Ball, Magazine Rifle, Mark I Solid Case, .303inch was first introduced in 1889, as the standard ammunition for the Lee-Metford rifle. The original round was a 215 grain round-nosed cupro-nickel jacketed bullet propelled by 71.5 grains (4.63 g) of RFG2 Blackpowder, giving it a muzzle velocity of 1830 feet per second (560 m/s) and a chamber pressure of about 19 short tons force per square inch (260 MPa). Since blackpowder is not very dense, the charge had to be pressed into a solid pellet to fit inside the round. While the rimmed cartridge made it easy to extract spent rounds from the chamber, it also made stacking rounds in the magazine more difficult, encouraging double feeds if the magazine was loaded without care.
Cordite was used as a propellant from 1891 and the first adopted cordite cartridge, the Cartridge S.A. Ball, Magazine Rifle Cordite Mark I, used the same bullet but delivered 1970 ft/s (600 m/s) at a chamber pressure of about 35,000 pounds per square inch (240 MPa). Small changes to the bullet jacket resulted in the Mark II (black powder) and Mark II.C (cordite) versions.
Nitrocellulose (first used as a propellant in 1894) was unsuitable for use in the Lee-Metford due to the higher temperatures and chemical activity. The Lee-Enfield was introduced to address these problems. Although not officially adopted until 1916, nitrocelulose rounds were widely used during the First World War, although cordite-loaded rounds were still produced for use in the tropics, where it was considered to be somewhat more stable.
The round nose bullet was found to be less effective in British service than Dum Dum rounds issued in limited numbers on the North West Frontier of India in the late 1890s. This led to the introduction of the Cartridge S.A. Ball .303 inch Cordite Mark III, basically the original 215 grain (13.9 g) bullet with the jacketing "cut back" to expose the lead in the nose. Similar hollow point bullets were used in the Mark IV and V rounds, the primary production versions. These soft nosed and hollow pointed bullets were later outlawed in the St. Petersburg Declaration and the Hague Convention, and in 1903 they were withdrawn from active service and were afterwards to be used for target practice until stocks ran out. To replace them the Mark VI round was introduced in 1904, using a round nose bullet similar to the Mark II but with a thinner jacket. It was generally agreed to be unsatisfactory.
In 1905 Mauser changed bullet design completely with the introduction of their "spitzer" rounds, the first of the classic design now referred to universally as "bullet shaped". In addition to being pointed, the round was also much lighter in order to deliver a higher muzzle velocity. It was found that as velocity increased the bullets suddenly became much more deadly, an effect later explained by hydrostatic shock and cavitation when the round hit.
The British took the opportunity to replace their Mark VI rounds with the new Mark VII, using a 174 grain (11.3 g) pointed bullet that gave a muzzle velocity of 2440 ft/s (740 m/s). In fact the Mark VII was considerably different than earlier designs, or the spitzer for that matter. In order to lower the weight they made the front third of the interior of the bullet out of aluminium instead of lead. While similar weight savings could have been had by using a single lighter material, such as steel, the design was deliberate in order to make the bullet "tail heavy". When flying through air the stability of the bullet was marginal, but when it rapidly decelerated when hitting a target, the heavier lead base wanted to "swap ends", causing the bullet to tumble and greatly increase damage. The Mark VII round remained the standard for the remainder of the .303 service life.
In 1938 the Mark VIII round was approved to obtain greater range from the Vickers machine gun. The primary change was the addition of a boat-tail and slightly more propellant, giving a muzzle velocity of 2550 ft/s (780 m/s) and somewhat better ballistics. Chamber pressure was higher, at 40,000–42,000 lbf/in² (about 280 MPa), making it suitable for firing only from the machine gun.
Tracer, armour piercing and incendiary cartridges were introduced during 1915, and explosive bullets in 1916. These rounds were extensively developed over the years and saw several Mark numbers. The last tracer round introduced into British service was the G Mark VIII round in 1945, the last armour piercing round was the W Mark 1Z in 1945, and the last incendiary round was the B Mark VII introduced in 1942. Explosive bullets were not produced in the UK after 1933 due to the relatively small amount of explosive that could be contained in the bullet limiting their effectiveness, their role being successfully fulfilled by the use of Mark 6 and 7 incendiary bullets.
In 1935 the .303 O Mark I Observing round was introduced for use in machine guns. The bullet to this round was designed to break up with a puff of smoke on impact with a target or the ground. The later Mark VI and VII incendiary rounds could also be used in this role if required.