.338 Lapua Magnum

In 1983, Research Armament Industries (RAI) in the United States began development of a new, long-range sniper cartridge capable of firing a 16.2-gram (250 gr), 0.338-inch (8.6 mm) diameter bullet at 914 metres per second (3,000 ft/s), that could lethally penetrate five layers of military body armor at 1,000 m (1,094 yd). After preliminary experiments, a .416 Rigby case necked down to take a 0.338-inch (8.6 mm) bullet was selected, since this diameter presents an optimum of sectional density and penetrating capability for practical spin-stabilized rifle bullets (bullets up to about 5 to 5.5 calibers in length).

The .416 Rigby is an English big game cartridge that was designed in 1911 to accommodate 325 MPa (47,137 psi) pressures. One of the disadvantages of these old cartridge cases, which were intended for firing cordite charges instead of modern smokeless powder, is the thickness of the sidewall just forward of the web. During ignition, the cartridge's base, just forward of the bolt face, is not supported.