.338 Lapua Magnum
The AWM in the .338 Lapua Magnum (8.6 x 70 mm) calibre was designed as a dedicated long range sniper rifle combining the maneuverability of rifles chambered in 7.62x51 mm NATO with the greater power and range of the .50 BMG cartridge.
Compared to most .50 calibre rifles, the AWM offers considerably less rifle weight, recoil, muzzle flash, smoke and report. Although the .338 Lapua Magnum delivers less kinetic energy to the target compared with the .50 BMG, both cartridges have similar trajectories, resistance to wind drift and penetration, while the .338 Lapua Magnum unquestionably outperforms the 7.62x51 mm NATO and .300 Winchester Magnum, especially at ranges beyond 800 metres (875 yd) and 1,100 metres (1,203 yd). AWSM rifles in .338 Lapua Magnum can also be deployed against unarmoured hard targets, including armoured glass.
The AWM .338 Lapua Magnum is fitted with a stainless steel, fluted, 686 mm (27") barrel, which research has found to be the best compromise between muzzle velocity on the one hand, and weight and length on the other. The rifle's barrel has an unconventional 279 mm (1:11 in) right-hand twist rate, optimized for firing .338-calibre very-low-drag bullets up to 16.85 g (260 gr). When the AWSM was developed military issue cartridges were loaded with 16.2 g (250 gr) very-low-drag bullets. Longer, heavier very-low-drag bullets like the Sierra HPBT MatchKing .338-calibre 19.44 g (300 gr) and the 21st century 19.44 gram (300 grain) .338-calibre HPBT Scenar can be used, but require a 254 mm (1:10 in) twist rate to stabilize them under high air density conditions as found on arctic coasts.
A problem with AWM rifles is that .338 Lapua Magnum cartridges loaded to the Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives (C.I.P.) maximum allowed overall length of 93.50 mm (3.681 in) do not function properly due to a lack of internal magazine length. The reason for this problem is that the AWSM bolt action is not specifically designed for the fat and long .338 Lapua Magnum cartridge. Ammunition manufacturers produce .338 Lapua Magnum cartridges that are loaded short enough (≈ 91.44 mm / 3.600 in) to fit in the 91.50 mm (3.602 in) long AWSM magazines. As long as .338 Lapua Magnum cartridges that will fit in the magazines are used, the AWSM rifles can be used as repeating rifles instead of single shot rifles.
To address the .338 Lapua Magnum ammunition length limitations of the AWM Accuracy International has since developed the AX338 long range rifle as the AWSM successor model. Compared to the AWSM, the bolt action of the AX338 is longer and wider and the internal magazine is lengthened, allowing the unimpaired use of .338 Lapua Magnum cartridges loaded to the C.I.P. (Permanent International Commission for the Proof of Firearms Portable) maximum allowed overall length of 93.50 mm (3.681 in). Further the AX338 has a 238 mm (1:9.375 in) twist rate to adequately stabilize longer, heavier .338 caliber very-low-drag projectile designs that became more common in the 21st century.
Ammunition types currently available for the .338 Lapua Magnum are FMJ, hollow point, Armor Piercing (AP) and Armor Piercing Incendiary (API).