FN SCAR History and Design . The US Special Operations Command ( US SOCOM ) issued a solicitation for the procurement of SOF Combat Assault Rifles ( SCAR ) on October 15 , 2003 . This solicitation requested a new combat rifle , specially tailored for the current and proposed future needs of the US Special Forces , which are somewhat different from latest generic US Army requirements , which are being fulfilled by the newest HK XM8 The key difference in basic requirements between XM8 and SCAR is that , while XM8 is a single - caliber weapon system , tailored for 5 . 56x45mm NATO ammunition , the SCAR should be available in various different calibers . Initial SOF requirements included two basic versions of SCAR system - the SCAR Light ( SCAR - L ) , available in 5 . 56mm NATO , and the SCAR heavy ( SCAR - H ) , which should be initially available in significantly more powerful 7 . 62x51 NATO chambering , and should be easily adaptable in the field to other chamberings . These other chamberings initially include the well - spread 7 . 62x39 M43 ammunition of the Soviet / Russian origins , and probably some others ( like the proposed 6 . 8x43 Remington SPC cartridge , especially developed for US Special Forces ) . The key idea of SCAR rifle system is that it will provide the Special Forces operators with wide variety of options , from short - barreled 5 . 56mm SCAR - L CQC variation , tailored for urban close combat , and up to long range 7 . 62x51 SCAR - H Sniper variant , as well as 7 . 62x39 SCAR - H , which will accept " battlefield pickup " Ak - 47 / AKM magazines with 7 . 62 M43 ammunition , available during the operations behind the enemy lines . Both SCAR - L and SCAR - H shall be initially available in three versions , Standard ( S ) , Close Quarters Combat ( CQC ) and Sniper Variant ( SV ; now it is dubbed Long Barrel - LB ) . All these variants , regardless the caliber and exact configuration , will provide the operator with the same controls layout , same handling and maintenance procedures , and same optional equipment , such as sights , scopes , and other current and future attachments . Late in 2004 US SOCOM announced , that the winner for the initial SCAR contracts is the FN USA , an US - based subsidiary of the famous Belgian company Fabrique Nationale Herstal . prototype rifles were manufactured by FN Manufacturing Inc , US - based subsidiary to FN Herstal ; This company will also handle series production of rifles . Starting mid - 2005 , first SCAR rifles went to end users in US Special Operation Forces . Since US SOCOM uses Navy - type " mark " designations , SCAR rifles were officially designated as 5 . 56mm Rifle Mark 16 ( SCAR - L / Light ) and 7 . 62mm Rifle Mark 17 ( SCAR - H / Heavy ) . It is believed that Mk . 16 and Mk . 17 rifles will gradually replace most rifle systems now in service with US SOCOM forces , such as M4 carbines , M - 16 rifles , M14 rifles and Mk . 25 sniper rifles . As it turned out , FN SCAR rifles are not based on any previous weapons but designed from the scratch . In all variants FN SCAR rifles feature gas operated , short stroke piston action with rotating bolt locking . Bolt system appears to be somewhat similar to that of FN Minimi / M249 SAW machine gun . This system apparently is less sensitive to fine sand , dust and any other fouling inside the receiver , than any system with M16 - type multi - lug bolt and plunger - type ejector . Receiver is made from two parts , upper and lower , connected with two cross - pins . Upper part is made from extruded aluminium , lower part is made from polymer . SCAR - L and SCAR - H use similar upper receivers that differ only in the size of ejection port . Other different parts include caliber - specific bolt , barrel , and lower receiver with integral magazine housing . Parts commonality between SCAR - L and SCAR - H is astonishing 90 % . Barrels are quick - detachable , and held in the upper receiver with two cross - bolts . Barrel change procedure requires minimum amount of tools , takes just several minutes and there is no need to adjust the headspace after the change . The trigger unit with ambidextrous safety - fire mode selector switch allows for single shots and full automatic fire , with no provisions for limited - length bursts mode . The charging handle could be easily installed on either side of the weapon , so the upper receiver has respective cuts on both sides . Top of the upper receiver is covered by the full - length integral Picatinny rail ( MIL - STD 1913 ) ; additional Picatinny rails are mounted on both sides and under the free - floating handguards . Side - folding polymer buttstock is adjustable for length of pull , and is shaped to provide positive cheek rest with adjustable cheek support . SCAR rifles are fitted with removable , adjustable iron sights , with folding diopter - type rear sight on the receiver rail , and folding front sight on the gas block . Any additional type of sighting equipment , necessary for current tasks , including telescope and night sights , can be installed using MIL - STD 1913 compatible mounts . Mk . 16 SCAR - L rifle will use improved M16 - type magazines , made of steel ; Mk . 17 SCAR - H will use proprietary 20 - round magazines in 7 . 62x51 NATO chambering , or standard AK - type magazines in proposed 7 . 62x39 M43 chambering . Current prototypes of SCAR rifles do not have bayonet mounts , and , probably , will never have one .