Barrett Rec 7.

Unlike possible replacements for the M16/M4 such as the now canceled XM8, the REC7 is not an entirely new rifle, instead it is only made up of an upper receiver (made by Barrett) that is attached to M16/M4 service rifle lower receivers and is compatible with many accessories intended for the M16/M4 family. It can also be mated to M16/M4 lower receivers currently in the possession of the US military. The rifle uses a short stroke piston mechanism, unlike the M16 or M4 which use direct impingement.

In addition, the REC7 uses the new 6.8 mm Remington SPC (6.8 x 43) cartridge, a round that is of roughly equivalent length to 5.56 mm ammunition, making it compatible with the M16 and M4 rifle magazines currently in use by the United States Military. According to Barrett, the new 6.8 mm round boasts 50% more stopping power than the 5.56 mm round and a longer effective range. The round has a slightly lower velocity than the 5.56 mm round, however Barrett claims it has 1.5 times the kinetic energy of the 5.56 mm round. The company claims that it is effective at six hundred meters and has a muzzle velocity of 2650 feet per second when fired from a 16 inch barrel. Like many AR-15 type rifles, such as the M16/M4, the barrel is threaded to allow muzzle attachments such as a suppressor. The REC7 employs the S.I.R. handguard (Selective Integration Rail) manufactured by ARMS Inc, which allows many military accessories such as a bipod, night vision devices, and combat optics to be placed on the rifle. In addition the SIR system has flip-up iron sights already built in to the system for when the weapon is used as a stand alone rifle.

Lolz nice copy 'n' paste dontcha think? Heres a pic: