SR - 25 The SR - 25 ( Stoner Rifle - 25 ) is a semi - automatic sniper rifle designed by Eugene Stoner and manufactured by Knight ' s Armament Company . The SR - 25 uses a rotating bolt and a direct impingement gas system . It is loosely based on Stoner ' s AR - 10 , rebuilt in its original 7 . 62×51mm NATO caliber . Up to 60 % of parts of the SR - 25 are interchangeable with the AR - 15 and M16 — everything but the upper and lower receivers , the hammer , the barrel assembly and the bolt carrier group . SR - 25 barrels were originally manufactured by Remington Arms with its 5R ( 5 grooves , rounded ) rifling , with twist 1 : 11 . 25 ( 1 complete turn in ) . The heavy barrel is free - floating , so handguards are attached to the front of the receiver and do not touch the barrel . First military purchase was spearheaded by the US Navy in the early 1990s ; the first operational deployment and use of the SR - 25 sniper rifle was with US Navy SEAL snipers supporting operations in Somalia in 1993 . Design . The SR - 25 enhanced match rifle utilizes the newer URX II Picatinny - Weaver rail system , rather than the older Mk 11 free - floating RAS , on the top of the receiver to accept different scope mounts or a carrying handle with iron sights ( front sight mounted on the rail located on the forward end of the non - modular handguard ) . The match version is designed to shoot at a precision of 0 . 5 minutes of angle , which corresponds to groups at . The Mk 11 Mod 0 system comes in 7 . 62 mm NATO caliber , and is designed for match - grade 7 . 62×51mm NATO ammunition . The Mk 11 system includes the rifle , 20 round box magazines , QD ( Quick Detachable ) scope rings , Leupold Mark 4 Mil - dot riflescope , Harris swivel - base bipod on a Knight ' s mount , and QD sound suppressor , which is also manufactured by Knight ' s Armament Co . Flip - up BUIS ( Back up iron sights ) are attached to the modified gas block and upper receiver . The Mk 11 Mod 0 utilizes an Obermeyer match target barrel , along with a RAS ( Rail Accessory System ) fore - end made by KAC , consisting of an long match fore - end . The RAS allows for quick attachment / detachment of MIL - STD - 1913 components . The aluminum fore - end makes no contact with the barrel forward of the receiver , allowing for extreme accuracy . The Mk 11 Mod 0 has an empty weight of , and an overall length of . The civilian version , using the longer match barrel , is guaranteed to produce groupings of less than at , or 0 . 3 angular mil , using factory match loads . During the Iraq War , the United States Marine Corps ordered 180 Mk 11 Mod 1 rifles . These were Mk 11s equipped with the upper receiver of the M110 Semi - Automatic Sniper System . The M110 upper gave the Mk 11 Mod 1 a URX modular rail system and a flash suppressor on the barrel . These saw limited use before they were phased out when the Marines chose to purchase the Mk 11 Mod 2 , which was simply the USSOCOM and U . S . Navy designation for the complete M110 rifle . The new SR - 25 Enhanced Match ( E . M . ) Carbine is very similar to the KAC M110 Semi - Automatic Sniper System , though the M110 utilizes the newer URX Rail system , a length - adjustable fixed buttstock , and an integrated flash suppressor . Starting late 2011 , USMC snipers will replace Mk 11 Mod 0 rifles with the M110 on a one - for - one basis .