Bushmaster ACR The Bushmaster ACR is an American prototype assault rifle created to the ACR Program made to replace the M - 4 Carbine and the M - 16 . It was initially a Magpul project however the project was brought by the Bushmaster industries . Description . The Masada rifle was developed by US - based company Magpul Industries , which became famous for its line of aftermarket accessories and replacement parts for firearms . Work on the new modular rifle , suitable for civilian , police and military applications and designed more or less along the lines of the SCAR program commenced in 2006 . First prototypes were shown to the public in 2007 at ShotShow , and early in 2008 it was announced that new rifle ( previously known as Masada ) will be mass - produced by famous American gun - making company Bushmaster Firearms . Current plans are to introduce civilian and police ( semi - automatic ) versions in mid - 2009 , with military select - fire version scheduled for production in late 2009 . It is also planned to introduce Masada / Bushmaster ACR rifles in 5 . 56mm / . 223 Remington caliber ; other calibers might follow later . Magpul also is developing a 7 . 62x51 / . 308 Winchester version of the Masada / ACR rifle , provisionally known as Masoud . It is still in early development and no information is available on its date of release to the public . The Masada / Bushmaster ACR rifle is gas operated , semi - automatic or selective - fired ( Military version only ) weapon of modular design . It utilizes aluminum alloy upper receiver , with polymer pistol grip / trigger / magazine housing ( lower receiver ) unit which is attached to the upper receiver using cross - pins . Various types of lower receivers are planned to accommodate different types of magazines ( i . e . AR - 15 type magazines as opposed to AK - type magazines ) . The trigger / manual safety unit is made as a single removable item , and it mostly utilizes Ar - 15 - compatible parts . The barrels of ACR / Masada are quick - detachable , with short - stroke gas pistons attached to each barrel . To remove the barrel ( for change , inspection or maintenance ) , user has to remove polymer handguards , then swing down the wire lever , located below the barrel , turn the barrel to unlock and pull it forward and out of the receiver . All barrels are free - floated within handguards to achieve consistent accuracy . Bolt group also is made as a single unit , with captive return spring and rotary multi - lug bolt which locks directly to the barrel breech . The standard magazine housing , which is suited to accept AR - 15 type magazines , has ambidextrous magazine release buttons . The ambidextrous bolt stop release button is located at the front of the triggerguard . Safety lever is also ambidextrous , and charging handle can be installed on either side of the gun , depending on user preferences . Depending on the version ( or user preferences ) ACR / Masada rifle can be equipped with various Magpul - made buttstocks , fixed or side - folding , and adjustable for length of pull ( some also with adjustable cheek rest ) . Each Masada / Bushmaster ACR rifle gas integral Picatinny rail on the top of the receiver ; additional accessory rails can be installed on forend according to user preferences . Masada / Bushmaster ACR rifle can be fitted with removable iron sights , and / or with any optical or night sight with appropriate mounting .