Accuracy International AS50

The AS50 is a semi-automatic .50 BMG anti-materiel precision rifle manufactured by British firearms producer Accuracy International. It enables operators to engage targets at very long range with high accuracy using explosive or incendiary ammunition, and employs a gas operated semi-automatic action and muzzle brake, allowing for lower recoil than the AW50 bolt-action rifle and faster target acquisition.

Source: Wikipedia — Accuracy International AS50 (CC BY-SA 4.0)