Colt ACR

Lore & Background

The Colt ACR was Colt's submission to the U.S. DoD Advanced Combat Rifle program. The main differences from the M16A2 were its distinctive furniture: a handguard with a heat-resistant inner lining, vent holes for lightening and air cooling, and a thickened ring at the front end acting as a handstop. The handguard was topped with an elevated sight track rib with a white stripe to improve fast target acquisition. The pistol grip was longer and of a different profile, and the rifle featured ambidextrous fire control selectors, a removable scope, and a streamlined six-position telescopic stock. A flash-hider and a Muzzle Brake Compensator (MBC) were fitted to reduce recoil and compensate for muzzle climb. Internally, an oil spring buffer was added to the lower receiver to control the cyclic rate and reduce felt recoil; combined with the MBC, these changes reduced felt recoil by 40 percent compared to a standard M16A2.

The key design change was the use of duplex rounds—a single cartridge containing two bullets. Olin Corporation produced three different duplex rounds for testing. The first consisted of two tungsten projectiles in a long-necked case; the second used a standard-length case with two 1.7 g (27 gr), 4.0 mm (0.158 in) tungsten projectiles; the final entry was another standard-length case with two 5.7 mm (0.224 in) projectiles, one 2.3 g (35 gr) and the other 2.1 g (33 gr). The latter was selected for submission to the ACR trials. The duplex load increased the number of projectiles fired, which is the primary determinant of battlefield casualties, but significantly reduced accuracy, limiting the maximum effective range to 325 m (1,066 ft) and requiring the user to also carry traditional ammunition for long-range shots.

Reader's Guide

The Colt ACR was not a total loss despite the program's outcome. The scope used on the rifle went on to be offered by Elcan as the C79, a version of which was eventually adopted as the M145 Machine Gun Optic, used on a number of firearms, especially those from Diemaco (now Colt Canada). Additionally, during testing a small batch of stocks were cut down to a smaller size similar to a CAR-15 buttstock. One such example made its way to David Armstrong, who used it as a basis for the design of the SOPMOD stock; another went to Magpul. These indirect contributions—the optic and the stock design—extended the Colt ACR's influence beyond the failed ACR program. The rifle itself, with its duplex ammunition, represented an attempt to increase hit probability by firing two projectiles per trigger pull, but the accuracy penalty and the need to carry separate ammunition for longer engagements limited its practical advantage. The program concluded that none of the entrants, including the Colt ACR, achieved enough improvement over the M16 to justify the cost of adoption.

Did You Know?

• The Colt ACR's scope was later offered by Elcan as the C79, a version of which became the M145 Machine Gun Optic.
• A small batch of Colt ACR stocks were cut down to a CAR-15 size; one went to David Armstrong and inspired the SOPMOD stock, another went to Magpul.
• The Colt ACR used duplex rounds—a single cartridge with two bullets—to increase the number of projectiles fired.
• The Muzzle Brake Compensator and oil spring buffer reduced felt recoil by 40 percent compared to a standard M16A2.