Barrett M468  The Barrett M468 is a variant of the M4 Carbine, rechambered for a heavier and larger 6.8mm bullet for increased terminal performance. The designation of M468 stands for an M4 carbine chambered for the 6.8mm SPC cartridge. It was an attempt to create an optimal Special Operations close-to-medium range carbine for Close Quarter Battle (CQB). A 12-inch barreled micro-carbine and 16-inch barreled carbine version were created. Barrett ceased manufacturing the rifle in 2010. The standard M468 uses a regular forend whereas the M468A1 comes with an ARMS "Selective Integrated Rail" (SIR) accessory rail system with integral "flat-top" Picatinny Rail scope mount and 4-position forend, and a detachable ARMS Back Up Iron Sight folding rear iron sight. The Barrett gas block in front has an integral forward-folding iron front sight. The rifle can use either a solid M16A2-style stock or an optional M4-style 4-position collapsible stock and used an M16A2-style pistol grip. The original muzzle brake was a proprietary design with four vents (two on each side) for increased control. This was later replaced with an M16A2-style "birdcage" muzzle-brake on the later Barrett REC-7. This was so the REC-7 would use parts already in the supply chain and have compatibility with US- and NATO-standard rifle grenades and silencers. A proprietary Barrett-made silencer was available that was optimized for use with the 12-inch barreled version. The suppressor weighed 1 pound and was 12" long. The Barrett gas block contained a ratchet that steadied the suppressor while it was mounted. The suppressor screwed on clockwise and unscrewed counter-clockwise. The M468 could not use the same magazines as the AR-15/M16 family, so they designed their own. The Barrett magazine was made of steel rather than aluminum and had a steel follower rather than an aluminum or plastic one. The magazine used two magazine springs instead of one to maintain steady pressure and reliable feeding. The original 28-round magazine was designed to be the same dimensions and use the same web gear as the 30-round AR-15/M16 magazines. The larger 30-round Barrett steel magazines were an inch longer and weighed 5 ounces more (0.569 lbs. [258 grams] empty / 1.82 lbs. [0.825 kg.] full) than the standard AR-15/M16 aluminum magazine.