. 303 British . 303 British , or 7 . 7×56mmR , is a calibre ( with the bore diameter measured between the lands as is common practice in Europe ) rifle and machine gun cartridge first developed in Britain as a black - powder round put into service in December 1888 for the Lee - Metford rifle , later adapted to use smokeless powder s . It was the standard British and Commonwealth military cartridge from 1889 until the 1950s when it was replaced by the 7 . 62×51mm NATO . Cartridge Specification . Case measurements . 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 up to . Recommended bullet diameter for standard . 303 cartridges is . Gunpowder . The original . 303 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 . 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 . " Cordite " was a stick - type or ' chopped ' smokeless gunpowder composed of nitroglycerine , gun - cotton , and mineral jelly , while " Rifleite " was a true nitrocellulose powder , composed of soluble and insoluble nitrocellulose , phenyl amidazobense , and volatiles similar to French smokeless powders . Unlike " Cordite " , " Riflelite " was a flake powder , and contained no nitroglycerine . Excessive wear of the shallow Lee - Metford rifling with all smokeless powders then available caused ordnance authorities to institute a new type of barrel rifling designed to increase barrel life ; the rifle was referred to thereafter as the Lee - Enfield . After extensive testing , the Committee on Explosives selected " Cordite " for use in the Mark II . 303 British service cartridge . Bullet . The initial . 303 Mark I and Mk II service cartridges employed a 215 - grain , round - nosed , copper - nickel full metal jacketed bullet with a lead core . After tests determined that the service bullet had too thin a jacket when used with cordite , the Mk II bullet was introduced , with a flat base and thicker copper - nickel jacket . History and development . During a service life of over 70 years with the British Commonwealth armed forces the . 303 - inch cartridge in its ball pattern progressed through ten marks which eventually extended to a total of about 26 variations . The . 303 cartridge has seen much sporting use with surplus military rifles , especially in Australia , Canada , New Zealand and to a lesser extent , in the United States and South Africa . In Canada , it was found to be adequate for any game except the great bears . In Australia , it was common for military rifles to be re - barreled in . 303 / 25 and . 303 / 22 . In South Africa . 303 British Lee Enfield rifles captured by the Boers during the Boer War were adapted for sporting purposes and became popular with many hunters of non - dangerous game , being regarded as adequate for anything from the relatively small impala , to the massive eland and kudu . The Mk II round - nosed bullet was found to be unsatisfactory when used in combat , particularly when compared to the dum - dum rounds issued in limited numbers in 1897 during the Chitral and Tirah expeditions of 1897 / 98 on the North West Frontier of India . 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 Mk IV and Mk V loadings , which were put into mass production . The design of the Mk IV hollow - point bullet shifted bullet weight rearwards , improving stability and accuracy over the regular round - nose bullet . These soft - nosed and hollow - point bullets , while effective against human targets , had a tendency to shed the outer metal jacket upon firing ; the latter occasionally stuck in the bore , causing a dangerous obstruction . The Hague Convention of 1899 later declared that expanding bullets for use on humans were inhumane , and as a result the Mk III , Mk IV , and Mk V were withdrawn from active service . The remaining stocks ( over 45 million rounds ) were used for target practice . 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 . In 1898 , APX ( Atelier de Puteaux ) , with their " Balle D " design for the 8mm Lebel Cartridge , revolutionised bullet design with the introduction of pointed " spitzer " rounds . 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 . In 1910 , the British took the opportunity to replace their Mk VI cartridge with a more modern design . The Mark VII loading used a 174 - grain ( 11 . 3 g ) pointed bullet with a flat - base which gave a muzzle velocity of 2 , 440 ft / s , ( 740 m / s ) and a ballistic coefficient of . 467 . 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 bullet out of aluminium ( from Canada ) or " tenite " ( cellulosic plastic ) , wood pulp or compressed paper , instead of lead and 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 yaw violently and deform , thereby inflicting more severe gunshot wounds than a standard single - core spitzer design . In spite of this , the Mk VII bullet was legal due to the full metal jacket used according to the terms of the Hague Convention . The Mk VII ( and later Mk VIII ) rounds have versions utilizing nitrocellulose flake powder smokeless propellant s . The nitrocellulose versions — first introduced in World War I — were designated with a " Z " postfix indicated after the type ( e . g . Mark VIIZ , with a weight of 175 grains ) and in headstamp s . Mark VIII . In 1938 the Mark 8 ( Mark VIII and Mark VIIIz ) round was approved to obtain greater range from the Vickers machine gun . Slightly heavier than Mk VII bullet at , the primary difference was the addition of a boat - tail and more propellant ( 41 grains of nitrocelluose powder in the case of the Mk VIIIz ) , giving a muzzle velocity of 2 , 525 – 2 , 900 ft / s ( 780 – 884 m / s ) . As a result , the chamber pressure was significantly higher , at ( approximately 280 – 414 MPa ) , depending upon loading , compared to the of the Mark VII round . Cross - sectional images of Mk VIII ammunition indicate that its boat - tail bullet was long and gently tapered , providing a very high ballistic coefficient . Mk VIII ammunition was described as being for " All suitably - sighted . 303 - inch small arms and machine guns " but caused significant bore erosion in weapons formerly using Mk VII cordite , ascribed to the channelling effect of the boat - tail projectile . As a result it was prohibited from general use with rifles and light machine guns except in emergency . As a consequence of the official prohibition , ordnance personnel reported that every man that could get his hands on Mk VIII ammunition promptly used it in his own rifle . Tracer , armour - piercing and incendiary . Tracer and armour - piercing cartridges were introduced during 1915 , with explosive bullets derived from John Pomeroy ' s work introduced as the Mark VII . Y in 1916 . Several incendiaries were privately developed from 1914 to counter the Zeppelin threat but none were approved until the Brock design late in 1916 as BIK Mark VII . K Wing Cmdr . Brock RNVR was a member of the Brock fireworks - making family . 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 8 in 1945 , the last armour - piercing round was the W Mark 1Z in 1945 and the last incendiary round was the B Mark 7 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 taken by the use of Mark 6 and 7 incendiary bullets . In 1935 the . 303 O Mark 1 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 . The later Mark 6 and 7 incendiary rounds could also be used in this role . During World War I British factories alone produced 7 , 000 , 000 , 000 rounds of . 303 ammunition . Factories in other countries added greatly to this total . Japanese 7 . 7 mm ammunition . Japan produced a number of machine guns that were direct copies of the British Lewis ( Japanese Type 92 machine gun ) and Vickers machine guns including the ammunition . These were primarily used in Navy aircraft . The 7 . 7mm cartridge used by the Japanese versions of the British guns is a direct copy of the . 303 British ( 7 . 7x56R ) rimmed cartridge and is distinctly different from the 7 . 7x58mm Arisaka rimless and 7 . 7x58mm Type 92 semi - rimmed cartridges used in other Japanese machine guns and rifles . Note : standard Japanese ball ammunition was very similar to the British Mk 7 cartridge . The two had identical bullet weights and a " tail - heavy " design , as can be seen in the cut - away diagram . Military surplus ammunition . Military surplus . 303 British ammunition is often available , notably at gun show s and from online dealers . It may or may not have corrosive primers . Care must be taken to identify the round properly before purchase or loading into weapons . Cartridges with the Roman numeral VIII on the headstamp are the Mark 8 round , specifically designed for use in Vickers machine guns . Although Mark 8 ammunition works well in a Vickers gun , it should not be used in rifles because the boat - tailed design causes increased barrel wear . The boat - tailed bullet design of Mk 8 ammunition is not in itself a problem . However , when combined with the cordite propellant used in Mk 8 cartridges , which burns at a much higher temperature than nitrocellulose , there is increased barrel erosion . The cumulative effects of firing Mk 8 ammunition through rifles were known of during the Second World War , and British riflemen were ordered to avoid using it , except in emergencies . The best general - purpose ammunition for any . 303 military rifle is the Mark 7 design because it provides the best combination of accuracy and stopping power . There is no problem with using ammunition loaded with corrosive primers , providing that the gun is thoroughly cleaned after use to remove the corrosive salts . Commercial Ammunition and Reloading . Commercial ammunition for weapons chambered in . 303 British is readily available , as the cartridge is still manufactured by major producers such as Remington , Federal , Winchester , Sellier & Bellot , Prvi Partizan and Wolf . Commercially produced ammunition is widely available in various FMJ , soft point , hollow point , flat - based and boat tail designs — both spitzer and round - nosed . Reloading equipment and ammunition components are also manufactured by several companies . Dies and other tools for the reloading of . 303 British are produced by Forster , Hornady , Lee , Lyman , RCBS , and Redding . Depending on the bore and bore erosion a reloader may choose to utilize bullet diameters of . 308 " - . 312 " with . 311 " or . 312 " diameter bullets being the most common . Bullets specifically produced and sold for reloading . 303 British are made by Sierra , Hornady , Speer , Woodleigh , Barnes , and Remington . Where extreme accuracy is required , the Sierra Matchking HPBT bullet is a popular choice . Sierra does not advocate use of Matchking brand bullets for hunting applications . For hunting applications , Sierra produces the ProHunter in . 311 " diameter . The increasingly popular all - copper Barnes TSX is now available in the . 311 " diameter as a 150 gr projectile which is recommended for hunting applications by Barnes . With most rifles chambered in . 303 British being of military origin , success in reloading the caliber depends on the reloader ' s ability to compensate for the often loose chamber of the rifle . Reduced charge loads and neck sizing are two unanimous recommendations from experienced loaders of . 303 British to newcomers to the caliber . The classic FMJ bullets are widely available , though purchasers may wish to check whether or not these feature the tail - heavy Mk 7 design . In any case other bullet weights are available e . g . 150 , 160 , 170 , 180 and , both for hunting and target purposes . Hunting Use . The . 303 British cartridge is suitable for all medium - sized game , and is an excellent choice for whitetail deer and black bear hunting . In Canada it was a popular moose and deer cartridge when military surplus rifles were available and cheap ; it is still used . It has been used as a hunting cartridge in many countries .