In the late 1950s, Eugene Stoner designed the AR-10 battle rifle. It was accurate for an auto-loading rifle, but it lost the competition to the M14 rifle. The patent rights for the AR-10 and the AR-15 were sold to Colt's Manufacturing Company. Colt focused on the AR-15, giving others the ability to capitalize on the AR-10 system. In the early 1990s, Stoner joined Knight's Armament Company and continued his AR-10 design work. The end result was the SR-25 which improved the AR-10 design with M16A2 advancements and parts commonality. The original SR-25 was released in the early 1990s and had a heavy free-floating match grade barrel with a fiberglass handguard. It had a flat-top upper receiver with a Mil-Std 1913 rail for mounting optics and a 2-stage match grade trigger. The bolt carrier was similar to the AR-10's, being chrome plated and having a captive firing pin retainer pin. The SR-25 was designed specifically to fire open-tip match cartridges. Accuracy was guaranteed at or under 1 minute of angle. The SR-25 uses what has become colloquially known as SR-25 pattern magazines. At first, AR-10 type 20-round magazines were used, but they were later replaced by steel 20-round magazines. The United States Special Operations Command took interest in the SR-25, particularly its high magazine capacity and faster engagement time compared to bolt-action rifles. After some modifications, SOCOM adopted the SR-25 as the Mk 11 Mod 0 in May 2000. Changes included a shorter barrel that could fire M118 and M118LR 7.62×51mm NATO rounds and had a quick detachable sound suppressor mount. An free-floating handguard rail system allowed mounting accessories. Flip-up front sights and adjustable back-up iron sights were added, and an M16A2 stock and pistol grip were used. Beginning in mid-2011, SOCOM began divesting the Mk 11 Mod 0 from their inventory and replacing it with the SSR Mk 20, the sniper variant of the FN SCAR. The Mk 11 is to be completely replaced by 2017.
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. 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 is chambered for 7.62×51mm NATO and is designed for match-grade ammunition. The Mk 11 system includes the rifle, 20 round box magazines, QD scope rings, LeupoldMark 4Mil-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 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 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 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.
