The Compact Semi-Automatic Sniper System program began with a June 2014 Army request for proposals seeking a shorter, lighter semi-automatic sniper rifle to replace the original M110 Semi-Automatic Sniper System, which had been fielded since 2007 to 2008 and which infantry units found too long and heavy for close-quarters, vehicle and airborne work.³ Heckler & Koch won the resulting contract on April 6, 2016, worth up to $44.5 million for as many as 3,643 complete rifle systems at roughly $12,000 per rifle.⁴ The winning HK design retained the 7.62×51mm NATO chambering of the outgoing M110 but replaced its Knight's Armament SR-25 based operating system entirely with the G28's short-stroke gas piston action.

There is a second layer to the naming confusion that matters for anyone researching this rifle. The same 2016 Heckler & Koch contract produced two role configurations of one physical rifle family, not two separate weapons. The M110A1 CSASS is the dedicated sniper-role configuration, built around a Schmidt & Bender 3-20x50 PM II Ultra Short scope and a fixed-comb stock. The M110A1 Squad Designated Marksman Rifle (SDMR) is the squad-level marksman configuration of the identical base rifle, fitted instead with a SIG Sauer TANGO6 1-6x24 low-power variable optic for closer engagement distances.⁵ Both are Heckler & Koch products off the same G28-derived receiver. This article covers the CSASS sniper-role configuration specifically, while noting where its facts overlap with the SDMR.

As a member of the wider family of designated marksman rifles, the M110A1 CSASS occupies the semi-automatic sniper-support niche between a bolt-action sniper rifle and a standard-issue service rifle, trading the M110 SASS's longer effective range for a shorter, lighter package suited to the same close-in and mobility-constrained scenarios that drove the original replacement requirement.

The G28/HK417-Derived Short-Stroke Gas Piston Action

The M110A1 CSASS chambers the 7.62×51mm NATO cartridge, the same round used in the outgoing M110 SASS, but the two rifles share almost nothing else mechanically.¹ Where the original M110 was a gas-operated rifle built on Eugene Stoner's SR-25 pattern, essentially a scaled-up AR-15 with a direct-impingement-influenced action, the M110A1 CSASS runs the HK417/G28 short-stroke gas piston system, with a rotating bolt cycling the action instead.¹ Heckler & Koch's own claim in period coverage was that the piston design runs cleaner and cooler than the older M110's operating system, a durability argument that lines up with the Army's stated goals for the competition. Debi Dawson, a spokesperson for the Army's Program Executive Office Soldier, said at the time the CSASS modifications were meant to improve reliability, durability, ergonomics and extended range performance relative to the M110.⁵

One deliberate weight-saving change separates the M110A1 from its German parent design. The Bundeswehr's own G28 uses a steel upper receiver. Heckler & Koch built the American CSASS variant with an aluminum upper instead, trimming weight for the U.S. Army's compact-rifle requirement.⁶ Feeding is by a detachable magazine holding 10 or 20 rounds of match ammunition, most commonly the 175-grain M118LR load, alongside the M80A1 Enhanced Performance Round and the XM1158 Advanced Armor Piercing Round.⁷

The rifle's barrel runs roughly 16.3 inches (414 mm), noticeably shorter than the M110 SASS's 20-inch barrel, and overall length is about 36 inches (910 mm) with the collapsible stock extended.⁴ Reported unloaded weight clusters around 8.4 lb (3.8 kg) in most sources, though GlobalSecurity.org cites a slightly heavier 9 lb (4.1 kg) and other outlets describe a combat-configured weight closer to 15 lb (6.8 kg) once the scope, suppressor and bipod are mounted.^1,4 The spread reflects that published figures often describe different accessory loadouts rather than a genuinely disputed base weight.

Optics, Suppressor and Furniture in the Sniper-Role Configuration

The sniper-role CSASS configuration pairs the rifle with a Schmidt & Bender 3-20x50 PM II Ultra Short scope, a high-magnification optic suited to the longer end of the compact rifle's engagement envelope, mounted on a Geissele optic mount over a Geissele M-LOK rail.⁶ That M-LOK rail was itself a running change. Heckler & Koch's earlier displays used the company's proprietary HKeyMod rail before switching to the industry-standard M-LOK interface the Army preferred.⁶ Standard equipment also includes an OSS SRM6 suppressor, a baffle-less design intended to control sound signature and muzzle flash without the added length of a conventional can, and a Harris 6-9 bipod for supported firing positions.⁶ The stock is collapsible with an adjustable cheek comb, letting the sniper set both length of pull and cheek weld to the mounted optic.¹

Effective range for the sniper-role CSASS configuration is cited around 800 meters, shorter than the roughly 1,000-meter figure often quoted for the M110 SASS it replaces, a direct trade-off for the shorter barrel and lighter overall package.³ Muzzle velocity with 175-grain M118LR ammunition runs close to 750 meters per second, with some sources citing figures nearer 780 m/s depending on barrel and load.¹

The table below is a targeted look at how the two role configurations of the same HK contract diverge.

Development traces to around 2012, when the U.S. Army began looking for a semi-automatic sniper rifle shorter and lighter than the M110 SASS after years of feedback from Iraq and the ongoing War in Afghanistan (2001-2021), where the M110's length was a persistent complaint in vehicles, buildings and during airborne insertions.³ The formal Compact Semi-Automatic Sniper System requirement was issued as an Army RFP in June 2014.⁴

Knight's Armament Company, the incumbent that had supplied the M110 since 2007 to 2008 and had seen that rifle named one of the Army's Best 10 Inventions of 2007, submitted an upgraded, shortened version of its own design, referred to internally as the M110K1.² It lost. Heckler & Koch won the CSASS contract on April 6, 2016, worth up to $44.5 million for up to 3,643 rifles, with an immediate order of 30 guns for testing.^4,7 Knight's Armament issued a public statement congratulating Heckler & Koch on the win, a notable gesture given the company was losing the successor contract to its own decade-old design.²

Heckler & Koch first displayed the finished M110A1 CSASS publicly at SHOT Show in January 2017, showing off the aluminum upper, OSS suppressor, Harris bipod and Schmidt & Bender scope that would define the production rifle.⁶ Fielding began in 2018, and the U.S. Marine Corps budgeted for 116 CSASS units to replace its own M110 rifles starting around May 2018, though press coverage of the Marine Corps rollout was notably more skeptical than the Army's, with headlines describing the service as not impressed and one report framing the CSASS as not the one they need.^9,10

In July 2019, the 82nd Airborne Division at Fort Bragg conducted operational trials of the M110A1, specifically valuing its shorter, lighter form for maneuverability immediately after a parachute jump, a scenario where the older M110 SASS's length was a known liability.¹¹ By the early 2020s the M110A1 SDMR configuration had been distributed far more widely than the dedicated sniper-role CSASS, with roughly 6,000 SDMR units fielded across Army and Air Force squads by around 2023, primarily replacing the M14-derived Mk 14 Enhanced Battle Rifle in the 300 to 600 meter squad marksman role.¹

Reporting from 2022 indicated the dedicated sniper-role CSASS configuration's fielding had been comparatively limited and its funding status uncertain, even as the SDMR configuration continued rolling out.¹² No source surveyed documents a named Special Operations unit adopting the CSASS sniper configuration specifically by name, so this article does not attribute one. Coverage instead centers on conventional Army airborne infantry and Marine Corps budget requests.

Documentation of the M110A1 CSASS in a specific combat engagement is thin. The rifle's fielding history is centered on conventional Army trials, such as the 82nd Airborne's 2019 airborne-infiltration exercises at Fort Bragg, and on Marine Corps procurement decisions rather than named operations.¹¹ Its fielding overlapped with the final years of the U.S. military drawdown from the War in Afghanistan (2001-2021) and the broader Iraq War and the War on Terror, but no source surveyed for this article confirms the CSASS sniper-role configuration specifically saw documented combat use in either theater, in contrast to the well-documented Iraq and Afghanistan combat record of the M110 SASS it replaced.⁸ Readers should treat any claim of a specific CSASS combat engagement with caution absent a named, sourced event.

The M110A1 program produced one physical rifle family in two role configurations, plus an unrelated Knight's Armament product that shares only a numeral with it.

• M110A1 CSASS, the sniper-role configuration covered by this article, Schmidt & Bender 3-20x50 optic, fixed-comb stock, roughly 800-meter effective range.⁶
• M110A1 SDMR, the squad designated marksman configuration of the identical Heckler & Koch base rifle, SIG Sauer TANGO6 1-6x24 optic, roughly 6,000 units fielded to Army and Air Force squads by 2023.¹

• Heckler & Koch G28, the Bundeswehr-service parent design, steel receiver, itself a designated-marksman derivative of the HK417 battle rifle, from which the M110A1 CSASS's action and layout descend.⁶
• M110K1, Knight's Armament's own competing CSASS entrant, an upgraded, shortened variant of its original M110 SASS. It lost the 2016 competition to Heckler & Koch and is not related to the M110A1 that resulted.²
• M110K1 6.5mm Creedmoor conversion, sometimes labeled M110A2 or M110A3 in press coverage, a completely separate Knight's Armament product. In October 2019, Naval Surface Warfare Center Crane awarded Knight's Armament an Indefinite Delivery, Indefinite Quantity contract worth roughly $15 million to convert SOCOM's existing original M110 SASS rifles to fire 6.5mm Creedmoor via new upper receivers.^13,14 This conversion is built on the SR-25 based design of the original M110 SASS. It does not share the Heckler & Koch G28 based design of the M110A1 CSASS or SDMR, and readers should avoid conflating the two despite the overlapping M110 naming.

The United States Army is the primary operator of the M110A1 CSASS, having run the original competition and fielded the rifle first to conventional infantry and airborne units, including the 82nd Airborne Division's 2019 trials.¹¹ The United States Marine Corps budgeted for 116 CSASS units beginning around 2018 to replace its own M110 SASS rifles, though Marine Corps press coverage of the rollout has been notably more mixed than Army coverage, with some outlets questioning whether the CSASS met the service's actual sniper requirement.^9,10

No source surveyed names a specific Special Operations Command unit fielding the M110A1 CSASS sniper configuration by name. Coverage of SOCOM's 6.5mm Creedmoor conversion program pertains to the separate, Knight's Armament-built M110K1/M110A2 conversion, not the Heckler & Koch CSASS, and this article does not extend that SOCOM association to the CSASS itself.¹³

Heckler & Koch's win over Knight's Armament's own upgraded M110 entry defines the M110A1 CSASS more than any single spec sheet number. Knight's Armament had built and supported the Army's semi-automatic sniper rifle since 2007, submitted its own shortened M110K1 for the 2016 competition, and still lost to an outside design built around the G28 and HK417.² The Army's stated reasoning centered on reliability, durability and ergonomics rather than a single headline figure, and the practical result was a rifle with a shorter effective range than the M110 SASS it replaced, in exchange for meaningfully less bulk.⁵

Set the two side by side and the differences are almost entirely mechanical rather than cosmetic. The M110 Semi-Automatic Sniper System runs a Stoner-pattern SR-25 operating system with a roughly 20-inch barrel and a longer, heavier combat-loaded profile, built for the maximum reach the 7.62x51mm NATO cartridge could deliver from a semi-automatic rifle. The M110A1 CSASS trades a chunk of that reach for a compact package built around the G28's short-stroke gas piston action and a 16.3-inch barrel, aimed squarely at the close-quarters, vehicle-borne and airborne scenarios where the older rifle's length was a genuine operational complaint rather than a mere preference.³

The M110A1 SDMR configuration adds a third comparison point worth naming, even though it is the same physical rifle as the CSASS rather than a rival. The SDMR was built specifically to replace the M14-derived Mk 14 Enhanced Battle Rifle in the 300 to 600 meter squad marksman role, a shorter-range mission than the CSASS's own sniper-support niche, illustrating how the single 2016 Heckler & Koch contract actually displaced two separate older rifles from two separate designs at once.¹

Who makes the M110A1 CSASS? Heckler & Koch, a German firm, manufactures the M110A1 CSASS. It is not built by Knight's Armament Company, despite carrying the same M110 family name as the earlier Knight's-built M110 Semi-Automatic Sniper System it replaced.^1,4

Is the M110A1 CSASS the same rifle as the M110A1 SDMR? Yes, in the sense that both are Heckler & Koch G28-derived rifles from the same 2016 Army contract. The CSASS is the sniper-role configuration with a Schmidt & Bender 3-20x50 scope, while the SDMR is the squad-marksman configuration with a SIG Sauer TANGO6 1-6x24 optic. They differ in optic, stock and intended engagement range, not in manufacturer or base action.⁵

What caliber does the M110A1 CSASS fire? The M110A1 CSASS is chambered in 7.62×51mm NATO, most commonly firing 175-grain M118LR match ammunition, along with the M80A1 Enhanced Performance Round and the XM1158 Advanced Armor Piercing Round.⁷

How much does the M110A1 CSASS cost? The original 2016 Heckler & Koch contract was worth up to $44.5 million for as many as 3,643 rifles, working out to roughly $12,000 per complete rifle system including optics and accessories.⁴

Is the M110A1 CSASS still in service? The M110A1 rifle family remains in U.S. service as of the early 2020s, though the dedicated sniper-role CSASS configuration has seen more limited fielding than the squad-role SDMR configuration, which had reached roughly 6,000 units distributed across Army and Air Force squads by around 2023.^1,12

What replaced the M110 SASS with the M110A1 CSASS? The Army ran a formal Compact Semi-Automatic Sniper System competition starting in 2014 specifically to find a shorter, lighter replacement for the Knight's Armament M110 SASS, which Heckler & Koch won in 2016 over Knight's Armament's own upgraded M110K1 entry.^2,4