The XM109, originally known as the Objective Sniper Weapon (OSW) or "Payload Rifle" (according to Barrett), is a semi-automatic anti-materiel rifle, designed primarily for engagement of light armored vehicles and similar materiel targets. The design uses the lower receiver from an M82/M107, but with a new upper receiver chambered in 25mm. In fact, it has been designed with this in mind. The upper receiver of the M82 rifles can be replaced with an XM109 upper receiver to form a fully functional XM109 rifle.
The 25 × 59 mm cartridge is used in the XM109 and the XM307 (product of the Objective Crew Served Weapon/OCSW program). As with the XM307, the XM109 can be reconfigured back to .50 BMG.
The XM109 offers greater range and a shorter overall length than the previous M82/M107 systems, as well as potentially greater power in the 25 × 59 mm cartridge over even the Mk 211 .50 BMG cartridge (AKA "Raufoss round").