M110A1 may refer to the M110A1 CSASS (Compact Semi Automatic Sniper System) or the M110A1 SDMR (Squad Designated Marksman Rifle).

However, several thousand M110A1 SDMRs have been fielded with the US Army and Air Force to replace various weapon systems currently being used.

In July 2012, the U.S. Army requested sources to remanufacture the current M110 rifle into the Compact Semi-Automatic Sniper System (CSASS).

The CSASS would 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.

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

Shortly after, an ECP (engineering change proposal) was announced which was speculated to be a sign of conversion of the CSASS to a squad designated marksman rifle configuration.

[11][12][13] The SDMR configuration was planned to give extended range capabilities to infantry squads so they could engage threats at distances of 300-600m.

[30] Meanwhile, the Navy and Marine Corps, which had expressed interest in the CSASS,[10] decided to instead pursue an M110 SASS PIP (Product Improvement Program) for FY2021 based on market research which indicated improved range and lethality with the PIP compared to the M110A1 CSASS without any increase in cost.

[31] Budget figures for FY2023 show funding set aside for the M110 SASS PIP to upgrade the Marine Corps' existing M110s.