The .303 British (designated as the 303 British by the C.I.P. and SAAMI) or 7.7×56mmR, is a calibre rimmed tapered bottleneck centerfire rifle cartridge. The .303-inch bore diameter is measured between rifling lands as is the common practice in Europe, which follows the traditional black powder convention.
It was first manufactured in the United Kingdom as a stop-gap black powder round put into service in December 1888 for the Lee–Metford rifle. From 1891, the cartridge used smokeless powder, which had been the intention from the outset, but the decision on which smokeless powder to adopt had been delayed. In CIP-regulated countries, every rifle cartridge combo has to be proofed at 125% of this maximum CIP pressure to certify for sale to consumers.
The measurement is the nominal size of the bore measured between the lands, which follows the older black powder nomenclature. Measured between the grooves, the nominal size of the bore is . Bores for many .303 military surplus rifles are often found ranging from around . Recommended bullet diameter for standard .303 British cartridges is .
Military use
History and development
During a service life of over 70 years with the British Commonwealth armed forces, the .303-inch (7.7 mm) cartridge in its ball pattern progressed through ten marks, eventually extending to about 26 variations.
The bolt thrust of the .303 British is relatively low compared to many other service rounds used in the early 20th century.
Propellant
The original .303 British service cartridge employed black powder as a propellant, and was adopted for the Lee–Metford rifle, which had rifling designed to lessen fouling from this propellant, which replaced the Martini-Henry rifle in 1888. Some Martini-Henrys were rebarrelled to use the new .303 as the "Martini–Metford".
The Lee–Metford was used as a trial platform by the British Committee on Explosives to experiment with many different smokeless powders then coming to market, including Ballistite, Cordite, and Rifleite. Ballistite was a stick-type smokeless powder composed of soluble nitrocellulose and nitroglycerine.
Mark II – Mark VI
thumb|left|upright|Longitudinal section of Mk VI ammunition 1904, showing the round nose bullet
The Mk II round-nosed bullet was found to be unsatisfactory when used in combat, particularly when compared to the "dum-dum" expanding bullet rounds issued in limited numbers in 1897 during the Chitral and Tirah expeditions of 1897–98 on the North West Frontier of India. The Mk III load, however, was almost immediately withdrawn as a result of production issues leading to the introduction of the similar Mk IV hollow-point loading in February of the next year, which was put into mass production in Britain, Canada and New Zealand.
To replace the Mk III, IV, and V, the Mark VI round was introduced in 1904, using a round nose bullet similar to the Mk II, but with a thinner jacket designed to produce some expansion, though this proved not to be the case.
Mark VII
thumb|upright|right|Longitudinal section of Mk VII ammunition circa 1915, showing the "tail heavy" design
In 1898, Atelier de Construction de Puteaux (APX), with their "Balle D" design for the 8×50mmR Lebel cartridge, revolutionised bullet design with the introduction of pointed "spitzer" rounds. In addition to being pointed, the bullet 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.
In 1910, the British took the opportunity to replace their Mk VI cartridge with a more modern design. The Mark VII loading used a pointed bullet with a flat-base. The .303 British Mark VII cartridge was loaded with of Cordite MDT 5-2 (cordite MD pressed into tubes) and had a muzzle velocity of and a maximum range of approximately . The Mk VII was different from earlier .303 bullet designs or spitzer projectiles in general. Although it appears to be a conventional spitzer-shape full metal jacket bullet, this appearance is deceptive: its designers made the front third of the interior of the Mk 7 bullets out of aluminium (from Canada) or tenite (cellulosic plastic), wood pulp or compressed paper, instead of lead and they were autoclaved to prevent wound infection. This lighter nose shifted the centre of gravity of the bullet towards the rear, making it tail heavy. Although the bullet was stable in flight due to the gyroscopic forces imposed on it by the rifling of the barrel, it behaved very differently upon hitting the target. As soon as the bullet hit the target and decelerated, its heavier lead base caused it to pitch violently and deform. By tumbling, it inflicted more severe gunshot wounds than a standard single-core spitzer design. The Mk VII bullet was considered to be in compliance of the Hague Convention as its metal jacket completely covered the cores. The convention only prohibited "the use of bullets which can easily expand or change their form inside the human body such as bullets with a hard covering which does not completely cover the core...". It was noted by German Professor K. Stargardt in December 1914 that the Mk VII bullet would routinely "...disintegrate on the lightest contact with a firm body, such as a bone," resulting in an "explosive effect," and leaving artillery-like fragmentation in the body.