0, and M110 are based loosely on the original AR-10 developed by Eugene Stoner but feature additional refinements instituted by KAC to maximize parts commonality with the AR-15 design, improve weapon reliability, and increase accuracy. The main differences between the Mk 11 and M110 are improvements suggested by a user group meeting between NAVSPECWAR, USASOC and USA in 2007: The rail system used: the KAC Free Floated RAS on the Mk 11 is replaced by a URX modular rail system with integral folding front 600-meter backup iron sight. The M110 buttstock: fixed, though the buttplate is adjustable for length of pull to match user preferences. Adjustment can be made without tools via a notched hand-tightened knob on the right-hand side of the stock. This feature was added during the change from XM110 to M110. The fixed buttstock also features integral quick-detachable sling swivel sockets located on each side of the stock near the rear of the lower receiver. The addition of a flash hider to the barrel of the M110, which also necessitates a modified QD Suppressor unit similar to that on the Mk 11. The M110's use of KAC's one-piece 30 mm scope mount instead of two separate scope rings. On June 12, 2008, the M110 was ranked #2 on the U.S. Army's top ten inventions of 2007. According to performance specification (MIL-PRF-32316 (AR) w/AMENDMENT 1, 5 October 2009): 3.4.1.1.1 Accuracy. The distance between the mean point of impact of each shot group, both unsuppressed and suppressed, shall be not greater than 1.1 inches at 300 feet. 3.4.1.1.2 Dispersion. The average mean radius (AMR) (see 6.11), of each shot group shall be not greater than to 0.68 inches at 300 feet. All targets shall be fired on using M118LR ammunition or equivalent, using five (5) round groups. Sporting use In 2009, the M110 rifle and commercial equivalents were added to the list of NFA-legal US service rifles under rule 3.1.6 of the NRA High Power Rifle Rules. Replacement or reconfiguration of M110 In April 2011, according to Military.com, the U.S. Army issued a request to the private sector to reconfigure or replace the current Knight Armament M110 sniper rifle, alleging that the current version of the M110 was not functioning well in the field and, according to industry officials and users in the field, required significant maintenance and replacement of parts. The U.S. Army responded directly, claiming that the