The M110 SASS (Semi-Automatic Sniper System) is an anti-personnel sniping system developed and marketed by Knight's Armament Company of Titusville, Florida, USA. The firearm is part of a complete semi-automatic weapons package with the rifle as its key ingredient and accessories only broadening the tactical scope of the overall arrangement. Debuting in 2007, the weapon was born of a US Army need to replace the venerable Remington M24 Sniper Weapon System (SWS), a trusted and true bolt-action system firing the widely-accepted 7.62x51mm NATO cartridge. The key limitation with the M24 was when encountering target-rich environments such as those of urban Iraq since the US-led invasion of 2003. The bolt-action system proved limited in its overall engagement capabilities while forcing the sniper to rely on a secondary weapon for self-defense - thusly becoming something of a tactical liability in the field. A semi-automatic form was now sought that held an inherent repeat-fire function and fed from a higher-capacity magazine. In many ways, the new weapon would be more akin to that of a modern "Designated Marksman Rifle" (DMR) as opposed to that of a traditional "sniper" element, a capability usually handed to a squad-level operator and recognized in the British and Israeli militaries as "sharpshooter" while being known to US authorities as the "Designated Marksman".
Through a competition held in 2005, the Knight's Armament design was marked the winner and afforded the US Army designation of M110 "Semi-Automatic Sniper System" (SASS). The weapon retained the M24's 7.62x51mm NATO cartridge chambering though this was now fed through a 10- or 20-round detachable box magazine. Firing was via a semi-automatic action involving a gas-operated piston and rotating bolt. In many respects, the M110 was a highly-modified Armalite AR-10 offshoot with improved tactical functionality and logistical capabilities refined to help bring it more in line with the AR-15 family and similar firearms. The improved rate-of-fire and penetrative capabilities of the M110 would serve it well in an active combat zone with over five years of collected after-action battle reports used in its development.
Outwardly, the M110 mimicked the well-accepted lines of the long-running AR-10/AR-15/M16 family of automatic weapons. The fixed stock was plastic to reduce weight and integrated to the receiver which housed the required internals. The weapon featured a well-angled ergonomic pistol grip with the magazine well in its usual place ahead of the trigger group. A heavily perforated heat shield / hand guard ran ahead of the receiver and shrouded a good length of the barrel, leaving some exposed length ahead of the weapon. The muzzle was capped by a slotted flash suppressor while support for an optional sound suppressor was noted. The receiver, hand guard and heat shield all featured lengths of MIL-STD-1913 rail which allowed for use of various accessories to suite operator needs. In its usual configuration, the M110 was fitted with a standard XM151 3.5-10x variable scope atop the receiver with an adjustable, folding bipod under the gas cylinder. The weapon was cocked in the usual AR-15/M16 way through a pull handle system found at the extreme aft end of the upper receiver. The M110 operator could tote his rifle via strap across the back or over the shoulder in the usual way while a soft or hard case was shipped with the rifle as well as all applicable cleaning supplies and maintenance tools.
Initial M110 examples were delivered to US Army elements operating in Afghanistan in 2008 and results proved the weapon sound. The M110 was used operationally by the storied 82nd Airborne Division in Afghanistan. The 7.62x51mm NATO cartridge gave excellent penetrative capabilities at ranges beyond that of the standard 5.56mm assault rifles found in the US Army and the repeat-fire, semi-automatic function allowed for quick-reaction/quick-strike abilities not found with the M24 SWS. Use of accurized optics only helped in making the M110 a feared weapon amongst insurgents. Should the marksman himself become engaged or trapped by an advancing insurgent force, he could quickly turn his M110 into a dedicated semi-automatic assault rifle and fight his way through to safety - a feature not inherent in the bolt-action M24 SWS series. Additionally, with no bolt handle to manage, the marksman need only keep his eye trained on a subject and his finger near the trigger.
Despite its showing, the US Army never relinquished use of their large stock of M24 SWS weapons. Instead, the M110 was adopted alongside the type it was meant to replace, meaning that the proven bolt-action rifle was granted an extended stay on the modern battlefield. Considering the rise of the Designated Marksman at the squad-level since, this has proven a sound adjustment. The US Marine Corps has also found favor in the newer M110 and is featuring these alongside their older 1960s-era M40 family bolt-action rifles with the intent to replace the similar Stoner Mk 11 (SR-25) and M39 "Enhanced Marksman Rifle" (EMR) series in inventory with the M110.
Long term usage of the M110 has led the US Army to request a more compact and lightened version of the M110 to be issued to its designated spotters. The primary shooter will then be afforded the in-development .300 Winchester Magnum-chambered "XM2010 Enhanced Sniper Rifle (ESR)" which is intended to formally replace the M24 SWS family, a mission the M110 failed to accomplish. The XM2010 has seen limited service with US Army forces in Afghanistan since March of 2011.
UPDATE: On April 2nd, 2012, the US DoD announced a procurement contract for the M110 SASS from the Knights Armament Company totaling $24,909,740 (contract W15QKN-12-D-0029). The contract is expected to be completed in full by March 21st, 2017.
It was announced on April 1st, 2016 that the M110 was to be replaced by the competing Heckler & Koch "Compact Semi-Automatic Sniper System" (CSASS) - the primary reason cited by the U.S. Army being the need for a more compact, shorter, reliable, and lighter sniping platform for use by Designated Marksmen. Over 3,600 rifles are expected to be procured by the service. The CSASS is based on the existing HK G28 model chambered in 7.62mm NATO - which is the HK 417 in Designated Marksman Rifle (DMR) form.
The M110 is currently in service with the likes of Argentina (federal police), Armenia (special forces), Colombia (Army), Greece (special forces), Iraq (special forces), Mexico (special forces), Poland (special forces), Senegal (Army) and Turkey (special forces) as well as the United States.
October 2018 - The USMC has allocated funds in the 2019 budget to procure up to 116 M110A1 Compact Semi-Automatic System Systems (CSASSs) to succeed the original M110 models.