When the bolt-action rifle became the standard for military shoulder arms in the late 19th century, the British Empire and the United States replaced their .45-caliber single-shot rifles with medium-bore repeating rifles. Each adopted a rimmed cartridge of roughly .30 caliber firing a heavy roundnose bullet from a relatively simple, magazine-fed, bolt-action rifle. The .303 British dates to 1888 or 1889, depending on the source; the U.S. Army's .30-40 Krag cartridge was issued in 1892.
The .303 replaced the .577/450 Martini-Henry cartridge that had served the Empire for the previous 17 years, including the famous 1879 action at Rorke's Drift. Unlike the Krag that was in front-line service for roughly 11 years, the .303 British served the Empire for almost 70 years.
.303 British in the Beginning
The .303 British started as a blackpowder, jacketed-bullet cartridge- not the best combination. The bullet was a long, 215-grain FMJ RN over a pelleted charge of blackpowder. Most sources state the muzzle velocity was 1,850 fps from a 30-inch test barrel, the length used in original Lee-Metford Mk1 service rifles. Note that I included "long" in the bullet description. That bullet placed demands on rifle chambers that affected future development of .303 service ammunition.
The transition from blackpowder to smokeless powder happened quickly. About 1891 a bundle of cordite replaced the pellet of blackpowder and produced velocities up to 2,050 fps, similar to U.S. .30-40 Krag 220-grain service ammo. This also forced a change in how barrels were rifled to deal with rapid wear from high-temperature cordite gases.
Like most service cartridges that started life with heavy RN bullets, the .303 evolved to using lighter Spitzer-type FMJ bullets for higher velocity and flatter trajectory. Here is where the original 215-grain bullet design vexed the engineers. Early long-throated rifles were still in service. The new Spitzers were targeted to be in the 170- to 175-grain range but were considered too short for accuracy in long throats if conventional materials were used.
Designers pursued nonconventional means to make a bullet that was long enough to be accurate in long throats but still provided the desired velocity and maximum range improvements. The result was the 174-grain Mark VII bullet, a flatbase Spitzer FMJ that allowed about 2,450 fps from service rifles.
To make the Mark VII bullet longer, designers used a lightweight plug ahead of the lead core. Most references cite aluminum plugs, but other low-density materials like plastic, paper, and fiber were also employed. The change had a profound effect on terminal performance, whether by design or happenstance we'll never know. The Mark VII's center of mass was significantly offset to the rear by so much light material in the nose. Quite stable in air, it was quick to tumble on impact with soft tissue. The .303 British Mark VII cartridge remained in service from about 1910 until the cartridge was superseded by the 7.62mm NATO in 1957.
.303 British Today and Handloading
The .303 British is still a popular hunting cartridge in former and current British territories. It has always enjoyed a U.S. following, and every major U.S. ammomaker currently offers at least one loading. Hornady even sells a match load with a boattail hollowpoint bullet that, at 174 grains, closely matches the old Mark VII load. Handloaders will find that most component manufacturers still offer a modest selection of bullet styles and weights. Sierra even includes a match bullet.
Handloading is straightforward once you get one thing anchored in your brain: All common Lee-Metford and Lee-Enfield service rifles have one locking lug at the rear of the bolt. Bolt bodies compress along their long axis under recoil, and cartridge cases stretch at a point ahead of the rim. You must respect pressures and not try to get more than about two full-power firings from cases.
The SAAMI-recommended maximum average pressure for the .303 British is set at 45,000 CUP on copper crusher equipment and 49,000 psi on piezoelectric test gear. That is well below the .308 Winchester's 62,000 psi. However, propellants that are well suited to the .308 also work well in the .303 British. With 180-grain bullets, .303 handloads are within about 100 fps of the same bullet weight in the .308 and slightly ahead of 180-grain .300 Savage handloads.
With an eye on bullet selection, let's revisit the long bullet chamber throat issue. The SAAMI drawing of the .303 British chamber shows a slightly tapered freebore section 0.209 inch long behind a leade that is 0.306 inch long. That's a total of more than a half-inch, which is a lot compared to modern chambers and apparently dimensioned with long bullets in mind. If I was going for accuracy loads in this chamber, I would be testing 170- to 180-grain components. If Spitzers don't shoot well, I'd try the roundnose options. Fat noses get closer to the chamber throat walls. Your rifle will definitely have dietary preferences.
One very short bullet that surprised me during manual development was the Speer 0.311-inch, 123-grain Hot-Cor Spitzer for the 7.62x39mm cartridge. During a meeting where we planned the weekly shooting schedule, one of my techs asked if we should shoot that bullet in the .303 British. The consensus was generally "too short for the throat." The tech suggested a quick screening for accuracy, and I agreed. Speer's old SMLE test rifle posted rather nice iron-sight groups, some close to 2 MOA with the little bullet, so I gave the tech the go-ahead to include it in testing. The 123-grain bullet can achieve over 2,900 fps in the .303 British, and the bullet jacket was designed for 2,400 fps. Therefore, we recommended it for varminting and light-recoil practice.
The list of major conflicts in which British and Commonwealth forces used the .303 British cartridge includes two World Wars and nineteen others. That is an enviable record of service.