The XM109, originally known as the Objective Sniper Weapon (OSW) or as Barrett's "Payload Rifle," is a semi-automatic anti-material rifle, designed primarily for engagement of light vehicles and similar materiel targets. The design is in many ways simply a scale up receiver for the M82/M107 series of .50 caliber (12.7 mm) rifles currently in service with the US Army and USMC. In fact, it has been designed with this in mind, and the upper receiver of those rifles can be replaced with an XM109 upper receiver to form a fully functional XM109 rifle. The 25 x 59 mm cartridge is used in the XM109 and the XM307 (product of the Objective Crew Served Weapon/OCSW program. The XM109 is in development most likely to provide commonality of ammunition for better logistics should the XM307 systems be fielded, more or less phasing out .50 Caliber BMG (Browning Machine Gun). As with the XM307, the XM109 can be reconfigured back to .50 BMG should the need, necessity, or export market require it to be done (The XM312 crew served weapon is more or less a .50 BMG version of the XM307 and has some 70%+ parts commonality with the parent system).
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 x 59 mm cartridge over even the Mk 211 .50 BMG cartridge (aka "Raufoss round"). Because of the recoil system employed by Barrett, carried over from the earlier semi-automatic systems, the recoil is predicted to not be substantially more than its .50 BMG predecessors.