The designation M110A1 covers two role configurations of the same H&K rifle rather than two different weapons, and this has caused persistent confusion among collectors and soldiers alike.¹ The Compact Semi-Automatic Sniper System (CSASS) configuration, fitted with a Schmidt & Bender telescopic sight, was the original 2016 program built as a dedicated sniper-role replacement for the older M110 Semi-Automatic Sniper System. That sniper-role build kept the M110A1 CSASS name, while the SDMR configuration described below carries a lighter SIG Sauer TANGO6 optic and went to ordinary squads instead of dedicated sniper sections. By 2022, nearly every M110A1 actually delivered had been built out as an SDMR rather than a CSASS, so in current U.S. service the M110A1 name mostly means this squad-level rifle.¹

A frequent point of confusion is the manufacturer itself. Knight's Armament Company, maker of the original M110 SASS, was actually a losing bidder in the 2016 competition that produced the M110A1, alongside FN Herstal.² Knight's Armament has continued building and upgrading the older M110 SASS product line separately, including the later M110A2, a distinct Knight's product unrelated to the H&K-built M110A1 covered here.^11,12 The Army's squad-marksman concept itself did not start with the M110A1. It traces back through the Vietnam-era M21 Sniper Weapon System, the special-operations M25 Sniper Rifle, and the SR-25-derived M38 Designated Marksman Rifle, all descended from Eugene Stoner's SR-25 before the Army adopted an entirely different rifle family for the M110A1.¹⁰

The M110A1 SDMR is one of the more recent entries in the broader designated marksman rifle category, a class that also includes older U.S. rifles built on the battle rifle tradition of full-power semi-automatic weapons. It reached its first Army unit in June 2020 and its fielding across the active Army, Army National Guard, and Air Force largely wrapped up by late 2023, at roughly the same time the Army began discussing its eventual replacement.¹³

The HK417-Derived Gas Piston Action and Aluminum Upper

The M110A1's action is a gas-operated, gas-piston system with a rotating multi-lug bolt, tracing back through the HK417 to a short-stroke piston Heckler & Koch first used on the G36.⁹ That piston layout keeps combustion gas out of the receiver, unlike a direct-impingement AR-10-pattern rifle such as the original Knight's Armament M110 SASS, and was marketed as improving reliability and reducing fouling in sustained use.⁹ The bolt itself is a 7-lug design descended from the AR-10 pattern Eugene Stoner developed decades earlier, the same basic architecture underlying the SR-25 and its descendants.^9,10

Where the M110A1 departs from its German G28 parent is the receiver material. The G28 uses a steel upper receiver for the Bundeswehr's accuracy and durability standard, while H&K swapped in an aluminum-alloy upper for the U.S. rifle specifically to meet the Army's weight requirements during the 2016 competition.^1,2 That single substitution, alongside shortening the handguard and barrel assembly, cut roughly 2.5 inches (6 cm) and 3 pounds (1.3 kg) off the older M110 SASS the M110A1 replaced.²

The rifle fires 7.62x51mm NATO from 10- or 20-round translucent polymer detachable magazines compatible with the wider family of AR-10-pattern 7.62mm magazines.¹⁵ Cited muzzle velocity with 175-grain M118LR match ammunition runs 750 to 780 m/s depending on the source and exact barrel length measured, over a 16.3-inch (414 to 419mm) chrome-lined barrel with a fluted chamber to help reliability when suppressed.^15,1 Rifling is 4 grooves with a 280mm (1 in 11 inch) right-hand twist.¹⁵ Beyond M118LR, the SDMR is issued with M80A1 Enhanced Performance Round ball ammunition and the M1158 Advanced Armor Piercing round, the latter specifically able to defeat body armor that standard 5.56mm M855A1 cannot.⁵ Effective range in the squad-marksman role is cited at roughly 300 to 600 meters, the exact gap the SDMR program was built to close between an M4 carbine's practical range and a dedicated sniper team's.⁵

SIG Sauer TANGO6 Optic and the SDMR's Squad-Level Fire Control

The two M110A1 configurations are distinguished mainly by their optics and stocks rather than any deeper mechanical difference. The SDMR carries a SIG Sauer TANGO6 1-6x24 low-power variable optic, chosen for its wider field of view and faster target transitions in a squad's close-to-mid-range fighting, while the CSASS sniper-role build instead mounts a Schmidt & Bender 3-20x50 PM II Ultra Short telescope for precision work out to roughly 800 meters.^5,15 The lower-magnification TANGO6 package is also cheaper, one reason the follow-on SDMR-specific contracts ran close to $6,100 per rifle, well under the roughly $12,000 unit cost quoted for the original CSASS package.^5,7

The rifle's controls are fully ambidextrous, with a convertible charging handle and dual-side selector and magazine release, deliberately modeled on the M4/M16 manual of arms so infantry soldiers already familiar with a carbine need little extra training.⁵ A free-float Geissele M-LOK handguard surrounds the barrel, paired with a Geissele adjustable two-stage trigger, a Harris bipod, and backup iron sights fitted alongside the primary optic.^5,15 Standard issue includes the OSS SRM6 suppressor, a one-piece baffle-less design integrated into the weapon system rather than treated as an add-on accessory.⁵ The whole rifle is finished in tan, chosen to reduce infrared signature in the field rather than for cosmetic reasons.⁵

Fully assembled with optic and suppressor, the SDMR weighs roughly 11 to 15 pounds (6.35 to 6.8 kg) depending on the exact accessory load counted, against 8.4 to 8.8 pounds (3.8 to 4.15 kg) unloaded without optic or can.^15,5 Overall length runs from about 35.4 inches collapsed to 39.7 inches extended (899 to 1,009mm) on its 5-position adjustable stock.¹⁵

From a 2012 Market Survey to a 2016 Army Contract

The Army's Project Manager Soldier Weapons office, through Army Contracting Command - New Jersey at Picatinny Arsenal, issued a market survey in July 2012 looking to remanufacture or outright replace the aging M110 Semi-Automatic Sniper System.³ The program that came out of that survey, the Compact Semi-Automatic Sniper System, called for a shorter, lighter 7.62mm semi-automatic rifle with better reliability, ergonomics, and suppressor integration than the M110 SASS soldiers had been carrying since 2005.^3,10

A finalized request for proposals went out in June 2014 as a full-and-open, single-award indefinite-delivery/indefinite-quantity contract. Offerors could submit either an all-new rifle or a retrofit of the existing Knight's Armament M110, with the base requirement set at 30 systems for testing and an option period that could grow as large as 3,643 rifles.³ FN Herstal publicly unveiled its contender that October, a rebadge of the SCAR-based Mk 20 Sniper Support Rifle it had already sold to USSOCOM for a related but separate sniper-support mission.⁴

Eight bids came in overall. On 31 March 2016, the Army awarded Heckler & Koch Defense Inc. the CSASS contract, number W15QKN-16-D-0051, worth up to $44.5 million for as many as 3,643 rifles based on a modified G28.² The winning design beat out both FN Herstal's SCAR-based entry and Knight's Armament's own retrofit proposal for the very rifle it was meant to replace.² The Army retained the older M110A1 designation for the new H&K rifle purely to avoid opening a brand-new program of record, even though the new rifle shares essentially no parts with the Knight's Armament M110 SASS it succeeded.¹

The 2018 Decision to Field It at Squad Level

Rather than keep the new rifle purely as a sniper-role CSASS, the Army announced in March 2018 that it would field a squad-level configuration of the same H&K rifle, the Squad Designated Marksman Rifle, to ordinary infantry, scout, and combat-engineer squads rather than specialist sniper sections.⁵ This filled a real doctrinal gap. Standard 5.56mm M4 and M16 rifles are effective to around 300 meters and cannot reliably defeat modern body armor at longer range, while dedicated sniper teams remain a scarce, specialized asset not organic to every squad.^5,7 The SDMR was meant to close that gap out to roughly 600 meters and directly replaced the M14 EBR (Enhanced Battle Rifle), a modernized M14 units had used informally as a squad marksman weapon since around 2009, along with some 5.56mm M4s that had been filling the same ad hoc role.⁶

Heckler & Koch Defense Inc. announced the first shipment of M110A1 SDMRs, produced at its Columbus, Georgia plant, on 4 April 2020.¹ Soldiers of the 1st Armored Brigade Combat Team, 3rd Infantry Division, specifically 5th Squadron, 7th Cavalry Regiment, became the first Army unit to formally receive and qualify on the rifle, training at Fort Stewart, Georgia on 5 June 2020.^7,8 Sergeant Patrick Nissen, a scout with the unit, described the SDMR as an upgrade to the whole squad's capability, saying he found it comfortable and stable to shoot from a prone firing position.⁷ Army civilian weapons expert David Parris framed the program's purpose plainly, noting the Army had given squads a rifle precise enough to close the capability gap between a carbine and a dedicated sniper rifle.⁸

Fielding then spread through the Army National Guard. Virginia and Kentucky Guard soldiers of the 116th Infantry Brigade Combat Team trained on new SDMRs at Fort Pickett, Virginia, in mid-July 2021.¹ In April 2022, soldiers of the 2-113th Infantry Battalion and the 44th Infantry Brigade Combat Team, both New Jersey Army National Guard, live-fired the rifle at Joint Base McGuire-Dix-Lakehurst.¹⁴ Follow-on SDMR-specific contract awards in January 2019 and January 2020 covered a combined 5,851 rifles at roughly $6,100 apiece, and a spring 2020 contract modification added about $33.5 million on top of the original $44.5 million H&K award.¹ The U.S. Air Force completed fielding of 1,464 SDMRs to security forces, explosive ordnance disposal technicians, and pararescuemen by around April 2022, while the Army projected completing its own roughly 6,000-rifle fielding across active and Guard units by late 2023.^1,13

No confirmed reports of combat or operational engagement use turned up in researching this rifle. Its 2020 to 2023 fielding window falls after the drawdown of major U.S. ground combat operations in Afghanistan and Iraq, so the M110A1 SDMR should be treated as fielded for standard infantry service rather than combat-proven.

Even during active fielding, some soldiers and observers already viewed the 7.62mm SDMR as a stopgap. The Army has framed it explicitly as a bridge ahead of the Next Generation Squad Weapon program, which introduced the 6.8mm XM7 and XM5 rifles starting around 2023 and is meant to eventually take over both the M4's and the SDMR's roles.^13,14 One commenter on a 2022 Army training photo described the SDMR as somewhat dated next to the newer 6.8mm platform, a view that reflects the SDMR's position as an interim 7.62mm solution rather than a long-term program of record.¹⁴

The M110A1 program only ever produced two real configurations of the same rifle, distinguished by optics, stock furniture, and mission role rather than by receiver or action design.

• M110A1 CSASS - the original 2016 program configuration, a dedicated sniper-role replacement for the M110 SASS, fitted with a Schmidt & Bender 3-20x50 PM II Ultra Short scope and rated to roughly 800 meters.¹⁵
• M110A1 SDMR - the squad-level configuration actually fielded at scale from 2020 to 2023, fitted with a SIG Sauer TANGO6 1-6x24 optic and issued to ordinary infantry, scout, and engineer squads.⁵

Per Wikipedia's account of the program, as of 2022 essentially none of the delivered rifles had been built out in the original CSASS sniper configuration. Every unit that reached troops had been assembled as an SDMR instead, effectively orphaning the sniper-replacement mission the CSASS competition was originally meant to fill.¹ That leaves Knight's Armament's own, separate M110A2 as the actual sniper-role successor still being built under the older M110 SASS product line, alongside Knight's M110K1 conversion kits that rechamber existing SOCOM M110 rifles for 6.5 Creedmoor.^11,12

Because the SDMR effectively absorbed the CSASS mission by default, most references to the M110A1 in current U.S. Army and Air Force service describe the squad rifle covered in this article rather than the sniper-role build the 2016 contract was originally written for.¹

No further hardware variants exist beyond the SDMR and CSASS configurations. Heckler & Koch has not marketed a shortened carbine-length or export version of the M110A1 specifically, unlike some contemporaries, keeping the platform tied strictly to its original U.S. Army and Air Force contract requirements.¹⁵

The United States Army is the primary operator, fielding the SDMR to active-duty infantry, scout, and combat-engineer squads as well as several Army National Guard brigades, including the 116th Infantry Brigade Combat Team (Virginia and Kentucky Guard) and the 44th Infantry Brigade Combat Team (New Jersey Guard).¹

The United States Air Force fields the rifle to security forces personnel, explosive ordnance disposal technicians, and pararescuemen, having completed delivery of 1,464 units by around 2022.¹ Some reporting also describes elements of the U.S. Marine Corps using the platform, though the SDMR's core fielding runs through the Army and Air Force.⁶

Total planned fielding across both services runs to roughly 6,000 rifles, a modest number by U.S. small-arms standards, reflecting the SDMR's role as a squad-level supplement rather than a rifle meant to replace the M4 carbine outright.¹³ No export customers or foreign operators have been reported for the M110A1 in either configuration, unlike the older M110 SASS platform or the SR-25 family more broadly.

The M110A1 SDMR's most instructive comparison is its own predecessor, the Knight's Armament M110 Semi-Automatic Sniper System, because the size and weight difference between the two rifles is the entire reason the SDMR program exists in the first place. Fully suppressed, the older M110 SASS measured about 46.5 inches (1,181mm) overall, some 13 inches longer than an M4 carbine and 7 inches longer than an M16A4, a length soldiers found unwieldy for a rifle meant to be carried at squad or patrol level.¹⁰ The M110A1, in both its configurations, cuts roughly 2.5 inches and 3 pounds off that footprint, and unlike the M110 SASS, which stayed a scarce sniper-section weapon, the SDMR variant pushed 7.62mm precision fire down to squad density for the first time.^2,10

The second comparison worth making is internal, between the M110A1 SDMR and its own sibling, the M110A1 CSASS. Both come off the same Heckler & Koch production line under the same 2016 Army contract, and the distinction is a matter of role rather than mechanism. The SDMR's SIG Sauer TANGO6 optic trades magnification for field of view and speed at 300 to 600 meters, the range band a rifle squad actually fights at, while the CSASS's Schmidt & Bender scope pushes precision out to roughly 800 meters for a dedicated sniper-role mission that, in practice, has barely been fielded.^5,1 Both trace back through the same HK417-derived action, so unlike a genuine cross-manufacturer rivalry, the SDMR versus CSASS comparison is really a story about how the Army chose to spend the same rifle differently than it originally planned.

Set against the Army's own future plans, the SDMR's 7.62mm NATO chambering already looks transitional. The Next Generation Squad Weapon program's 6.8mm XM7 rifle is intended to eventually absorb the SDMR's designated-marksman role alongside the standard M4 carbine's, and some soldiers already described the 7.62mm SDMR as dated within two years of receiving it.¹⁴ That does not make the M110A1 SDMR obsolete today. It remains the U.S. Army and Air Force's fielded squad-level precision rifle, still well short of a formal replacement decision, and its 300 to 600 meter role and 7.62mm armor-piercing capability address a gap the 5.56mm M4 alone still cannot close.

What caliber does the M110A1 SDMR use

The M110A1 Squad Designated Marksman Rifle fires 7.62x51mm NATO, using M118LR match ammunition, M80A1 Enhanced Performance Round ball, and the M1158 Advanced Armor Piercing round for penetrating body armor.^5,15

Who manufactures the M110A1 SDMR

Heckler & Koch manufactures the M110A1 in both its SDMR and CSASS configurations, with major components made at H&K's Oberndorf am Neckar plant in Germany and final assembly at H&K Defense Inc.'s facility in Columbus, Georgia.^7,2

What is the difference between the M110A1 SDMR and the M110A1 CSASS

Both are the same Heckler & Koch rifle built under the same 2016 Army contract. The SDMR carries a SIG Sauer TANGO6 1-6x24 optic for squad-level fire out to about 600 meters, while the CSASS carries a higher-magnification Schmidt & Bender scope for a dedicated sniper role out to roughly 800 meters. By 2022, nearly all delivered rifles were in SDMR configuration.^5,1

Is the M110A1 SDMR still in service

Yes. The U.S. Army and Air Force completed most of their fielding of roughly 6,000 rifles by late 2023, and no replacement had formally entered service as of the SDMR's fielding window, though the Next Generation Squad Weapon's 6.8mm XM7 is expected to eventually take over its role.^13,14

How much does the M110A1 SDMR cost

Follow-on SDMR-specific contracts placed the unit cost at roughly $6,100 per rifle, lower than the approximately $12,000 quoted for the original CSASS sniper-role package, largely because the SDMR uses a cheaper optic.^5,7

What is the M110A1 SDMR's effective range

Around 300 to 600 meters in the squad designated marksman role, versus roughly 800 meters for the CSASS sniper-role configuration of the same rifle.⁵