The M468 is the designation for an upgrade to the M16/M4 family of assault rifles made by Colt. The M468 is manufactured by Barrett Firearms Company, who in addition to making this upgrade also makes the M82 .50 caliber sniper rifles in use by various branches of the United States Military.
Unlike possible replacements for the M16/M4 such as the now cancelled XM8, the M468 is not an entirely new assault rifle, instead the M468 is only made up of an assault rifle upper receiver (made by Barrett) that is attached to M16/M4 assault rifle lower receivers and is compatible to 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, thus causing the cost to update the M16/M4s to be significantly less than replacing all the M16/M4s in the US arsenal with a new weapon.
In addition the M468 uses the new 6.8 mm Remington SPC rounds that are very similar and size to the 5.56 mm rounds used by the United States Military today. According to Barrett, the new 6.8 mm round is supposed to have 50% more stopping power than the 5.56 round. However according to the company, it has a slightly lower velocity than the 5.56 round but has 1.5 times the kinetic energy as the 5.56 mm round. The company claims that it is effective at six hundred meters and travels at 2650 feet per second. The M468 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 had flip-up iron sights already built in to the system that can be used if used as a stand alone weapon.
According to Military.com the entire rifle costs $ 2,535 however the upper receiver upgrade kit alone only costs $ 1,494. The Barrett M468 page lists the complete rifle at $2,700 and the complete upper receiver at $1,590.
While information regarding US military use of the Barrett M468 is murky, it has been reported by several reliable sources that some weapons are in current, if limited, use by US SOF in the GWOT.