The Hellfocker M991 Sniper Weapon System is a full-calibre, semi-automatic sniper rifle/designated marksman rifle that is chambered for the 7.92x57mm ISTO round, designed and produced by the Hellfocker Arms Corporation. It is based on the M-150 Battle Rifle and shares 60% parts commonality with that weapon. The primary difference is a heavier, longer barrel, a differnt upper receiver and fire selector, a modified hand grip, and a completely different stock as well as the lack of a rearward iron sight. The weapon is designed to be used, as with the M-150, with a variety of rail-mounted accessories; most typically, a telescopic or electro-optical sight and a detachable bipod. The barrel can mount a suppressor, which is often utilised by special operations snipers.

Introduced in the late 3260s, it came to replace the SR-38 designated marksman rifle and the M7 sniper rifle by the early 3270s in Army and Marine inventories. It was subsequently adopted by police forces as a powerful, accurate sniper rifle capable of semiautomatic fire.

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