That, ladies and gentlemen, is the Barrett XM109 Payload rifle. The Barrett webpage tells us:
Providing Light Fighters with AP lethality out to 2000 meters, the Barrett XM109 25MM Payload rifle will allow soldiers to engage and quickly destroy enemy light armor. Like the M107 .50 caliber LRSR, the XM109 has accuracy, lethality and legendary Barrett reliability. The XM109 is destined to be a tremendous war fighting asset in the military arsenal. Full rifles or upper conversion units for the M107, including the bolt, upper receiver, and magazine, are available.If the anti-gunners don't like the Barrett .50 cal rifles, they'll really hate this one. If you have never seen what 25mm ammo can do to light armor, then you haven't been downrange with me at Peason Ridge. There are vehicles there that have been shredded by that stuff. The ammo comes in two flavors, if I remember correctly; AP and HE. Either one will do a number on light vehicles. This firearm is only available to the military. Still, I want one.
Ronnie Barrett just gave our boys a big boost.
Hat tip to Ravenwood.
UPDATE: For those of us who insist on inch designations, that 25mm comes to approx 0.984