Accuracy International AWM in .338 Lapua Mag.
The Arctic Warfare Magnum system
Main article: Accuracy International Arctic Warfare#Design details
The AWM rifle is a variant of the British Accuracy International Arctic Warfare (AW). Compared to the AW, the AWM has a longer bolt to accommodate larger magnum-length cartridges such as the .300 Winchester Magnum and the .338 Lapua Magnum.
The AWM features a detachable box magazine which holds five rounds. The normal cartridges for this rifle, and the ones which have been accepted by NATO for use in AWM rifles, are .300 Winchester Magnum and .338 Lapua Magnum.
Muzzle brakes are fitted to reduce recoil, jump and flash and act as a base for optional iron sights and suppressors.
Normally, the AWMs are outfitted with a Schmidt & Bender PM II 10x42 telescopic sight with 10x fixed power of magnification. However, a Schmidt & Bender PM II with variable magnification of either 3-12x50, 4-16x50 or 5-25x56 can be used if the operator wants more flexibility to shoot at varying ranges, or when a wide field of view is required. Accuracy International actively promotes fitting the German made Schmidt & Bender PM II product line as sighting components on their rifles, which is almost unique for a rifle manufacturer. The German and Russian Army preferred a telescopic sight made by Zeiss over Accuracy International's preference.
The AWM rifle is normally supplied in a metal transit case together with scope, mount, butt spacers, bipod, spare magazines, sling, cleaning and tool kits.
.300 Winchester Magnum
The .300 Winchester Magnum offers a flatter trajectory, and a significant increase in wind resistance and supersonic range over the 7.62x51mm NATO cartridge. Despite the cartridge's greatly increased muzzle velocity, it delivers greater precision than ordinary 7.62x51mm NATO ammunition and is only slightly eclipsed by the best match-grade 7.62x51mm NATO ammunition. This significantly enhanced range and precision ensures high first-shot hit probability to well beyond 800 m using standard .300 Winchester Magnum match grade ammunition. For precision shooting Federal Gold Medal Match is the most commonly used ammunition.
The AWM chambered for the .300 Winchester Magnum is fitted with a fluted, stainless steel barrel that is 660 mm (26") long for optimum velocity and nominal weight.
.338 Lapua Magnum
A Dutch ISAF sniper team displaying their Accuracy International AWSM .338 Lapua Magnum rifle and Leica/Vectronix VECTOR IV laser rangefinder binoculars.The AWM in the .338 Lapua Magnum calibre was designed as a dedicated long range sniper rifle combining the manoeuvrability of rifles chambered in 7.62 x 51 mm NATO with the greater power and range of the .50 BMG cartridge.
Compared to most .50 calibre rifles, the AWSM 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 7.62 x 51 mm NATO, especially at ranges beyond 800 m. AWSM rifles in .338 Lapua Magnum can also be deployed against unarmoured hard targets, including armoured glass.
The AWSM is fitted with a stainless steel, fluted, 686 mm (27") barrel, which research has found to be the best compromise between velocity and precision on the one hand, and weight and length on the other. A non-traditional 279.4 mm (1:11 in) right-hand twist rate was selected to optimize the rifle for firing 16.2 up to 19.44 gram (250 up to 300 grain) .338-calibre very-low-drag bullets. Whether this twist rate is adequate to stabilize 19.44 gram gram (300 grain) very-low-drag bullets in dense air encountered in Arctic sea level environments is questionable. The bullet manufacturer Sierra advises a tighter 254 mm (1:10 in) twist rate for its 19.44 gram (300 grain) .338-calibre HPBT MatchKing bullet.
A problem with AWSM rifles is that .338 Lapua Magnum cartridges loaded to the C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives) 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. Because of this, ammunition manufacturers produce .338 Lapua Magnum cartridges that are loaded short enough (≈ 91.44 mm (3.600 in)) to fit in the 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. Ammunition types currently (2007) available for the .338 Lapua Magnum are FMJ, hollow point, Armour Piercing (AP) and Armour Piercing Incendiary (API).