Barrett REC7 The Barrett REC7 ( designation stands for “ reliability - enhanced carbine ” 2007 ) is a M4 - pattern rifle available in either 5 . 56 NATO or 6 . 8 SPC . History . The REC7 is Barrett ’ s second AR - pattern rifle chambered for the 6 . 8 mm Remington SPC cartridge , the first being the Barrett M468 rifle . The 6 . 8 SPC - chambered M468 rifle employed the same direct gas - impingement system as the M4 . The result was a system that jetted hot gases directly into the rifle ’ s receiver , leading to potential stoppages if regular maintenance and cleaning protocols were overlooked . To enhance potential mechanical reliability , Barrett incorporated a short - stroke , piston - driven system that offers the potential for cleaner and cooler operation than one with direct gas - impingement . Barrett are still selling its limited stock of the M468 but only as an upper receiver kit and not as a complete rifle . Design and features . Unlike possible replacements for the M16 / M4 such as the now canceled XM8 , the REC7 is not an entirely new rifle , instead it is made up of an upper receiver that is attached to a M16 / M4 lower receiver 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 gas 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 × 43 mm ) cartridge , a round that is of roughly equivalent length to 5 . 56 mm ammunition , so it is compatible with a standard - size lower receiver currently in use by the United States military . According to Barrett , the new 6 . 8 mm round boasts 44 % more kinetic energy than the 5 . 56 mm round at ranges of 100 to 200 meters and a longer effective range . The company claims that it is effective at five hundred meters and has a muzzle velocity of 2650 feet per second when fired from a 16 inch barrel . The REC7 uses a short - stroke gas piston designed by Barrett . It rides above the barrel and is housed inside the fore - end . The spring - loaded piston is a one - piece 17 - 4 stainless steel rod . The forward and rearward movement of the piston is approximately one inch . Like many AR - 15 type rifles , such as the M16 / M4 , the barrel is threaded to allow muzzle attachments such as a suppressor ; it can also use M16 / M4 bayonet s on its muzzle , such as the M9 Bayonet or OKC - 3S Bayonet . The REC7 employs a free - floating Daniel Defense rail system , which allows many military accessories such as a bipod , night vision device s , and combat optics to be placed on the rifle . The REC7 features forged 7075 aluminum upper and lower receivers that are hard - coat anodized a deep black . The lower receiver has a single - stage trigger , a Magpul enhanced trigger guard for firing with gloves , and a beveled magazine well for rapid magazine changes . The upper receiver is flat - top with a Picatinny rail . The barrel is chrome - lined and is fitted with a M16A2 - style birdcage muzzle brake and pistol grip . The stock is a six - position Magpul MOE . The 6 . 8 SPC cartridge was designed to be used in standard AR lowers but 5 . 56 mm AR magazines cannot be used with the 6 . 8 mm round . Barrett has developed a magazine for its 6 . 8 SPC rifles that differs from the standard AR - pattern magazines . They are manufactured from steel and have a steel follower . The REC7 ’ s 30 - round magazine is about one - inch longer overall and weighs 5 ounces more than a standard AR magazine . Barrett also sell 10 - round 6 . 8 mm magazines . The REC7 outfitted in a shortened barrel PDW configuration was one of the weapons displayed to U . S . Army officials during an invitation - only Industry Day on November 13 , 2008 . The goal of the Industry Day was to review current carbine technology prior to writing formal requirements for a future replacement for the M4 carbine . The Barrett Enhanced Bolt is made from high - strength 9310 steel . The bolt is designed specifically for use in the piston operated REC7 , not just adapted from a direct gas bolt . The bolt ’ s gas - ring - free design is easy to clean . Reinforced at critical areas , every bolt is proofed and magnetic - particle inspected to guarantee reliable performance . At the heart of the operating system is a nitrided , two - position , forward - venting gas plug that retains the piston . The piston can be accessed through the front of the gas block without removing the handguard so optical sights or laser devices do not need to be zeroed after routine maintenance . The REC7 rifle ’ s forged 7075 aluminum upper and lower receivers are Type 3 hardcoat anodized . The lower houses an ultra - dependable single - stage trigger . The upper supports a free - floated , hammer - forged , chrome - lined barrel with M4 feed ramps machined into the receiver and the barrel extension . A mil - spec A2 flash hider protects the muzzle .