[3]On September 28, 2005, the Knight's Armament Co. rifle won the competition and was selected to be the supplier of the M110 Semi-Automatic Sniper System.

The XM110 underwent final operational testing in May and June of 2007 at Fort Drum, New York by a mix of Special Forces troops and Sniper trained soldiers from the 10th Mountain Division.

The SR-25, Mk 11 Mod 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: On June 12, 2008, the M110 was ranked #2 on the U.S. Army's top ten inventions of 2007.

[6] 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.

[7] The U.S. Army responded directly, claiming that the rifle was functioning perfectly, citing a 100% approval rating from the 173rd Airborne Brigade, and they were simply looking for a smaller, lighter version of M110 for the spotter in a sniper team.

The CSASS will be a shorter and lighter version of the M110 with a collapsible stock and removable flash suppressor, giving it an overall length of 36 inches (910 mm) and a weight of 9 pounds (4.1 kg) unloaded.

[11] On 1 April 2016, the Army announced it had awarded Heckler and Koch a contract with a maximum value of $44.5 million as winner of the competition to replace the KAC M110.

These conversion kits included complete upper receiver assemblies chambered for 6.5 Creedmoor as well as new muzzle brakes, and B5 Systems collapsible precision buttstocks.