The .303-inch bore diameter is measured between rifling lands as is the common practice in Europe which follows the traditional black powder convention.

According to official rulings of the Commission internationale permanente pour l'épreuve des armes à feu portatives (CIP), the .303 British can handle up to 3,650 bars (365.0 MPa; 52,940 psi) Pmax piezo pressure.

[5] 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.

[2] This means that .303 British chambered arms in CIP-regulated countries are, as of 2023[update], proof tested at 4,562 bars (456.2 MPa; 66,170 psi) PE piezo pressure.

[7] 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 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.

[9] The initial .303 Mark I and Mk II service cartridges used a 215-grain (13.9 g), round-nosed, copper-nickel full metal jacketed bullet with a lead core.

[12] This led to the 1898 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.

[12] 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 Swiss were concerned about small arms ammunition that "increased suffering", and the Dutch focused on the British Mark III .303 loading in response to their treatment of Boer settlers in South Africa.

Boer guerrillas allegedly used expanding hunting ammunition against the British during the war, and New Zealand Commonwealth troops may have brought Mark III rounds with them privately after the Hague Convention without authorization.

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, thereby inflicting more severe gunshot wounds than a standard single-core spitzer design.

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 bullet weight of 175 gr (11.34 g)) and in headstamps.

Although the round had better ballistics, troop trials in 1913 revealed problems including excessive recoil, muzzle flash, barrel wear and overheating.

[26] In 1938 the Mark VIIIz "streamline ammunition" round was approved to obtain greater range from the Vickers machine gun.

[31] As a consequence of the official prohibition, ordnance personnel reported that every man who could get his hands on Mk VIIIz ammunition promptly used it in his own rifle.

[35] Spent .303 cartridges were used to make cases of the bullet pencils included in some of the Princess Mary Christmas gift boxes given to troops in World War 1.

[36] Imperial Japanese Navy Air Service adopted Ro-Go Ko-gata seaplane armed with a .303 MG in 1918, and the calibre was common on surplus Entente aircraft acquired by the Imperial Japanese Army Air Service after WWI, so its usage continued during the Interbellum, and on naval aircraft even throughout WWII.

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.

A change.org petition asking Lithgow Arms to chamber the LA102 centrefire rifle in .303 as a special edition release has attracted considerable attention both in Australia and worldwide.

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, Denel-PMP, Prvi Partizan and Wolf.

The .303 British cartridge is suitable for all medium-sized game and is an excellent choice for whitetail deer and black bear hunting.

The .303 British can offer very good penetrating ability due to a fast twist rate that enables it to fire long, heavy bullets with a high sectional density.

[45] In 1899, the British service round was lengthened and necked-out to create the .375 Flanged Nitro Express hunting cartridge for single-shot and double rifles.

The ordinary round was designated "Cartridge S.A. ball .303 inch Rimless" despite the fact that it retained headspacing on its rim and was semi-rimmed.

After WWII, Australians found themselves with quite a few .303" service rifles but at the same time new legal restrictions on military ammunition, which led to development of many wildcat rounds,[47] the best-known of which are .303/25 and .303/22.