Colt ACR

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

The Colt ACR was Colt’s entry in the U.S. Department of Defense’s Advanced Combat Rifle program in the early 1980s. It did not prove to be a clear improvement over the standard M16, so none of the entrants won the program. Still, the ACR influenced later equipment: the scope developed for it appeared as the Elcan C79 (used on various firearms, including those from Colt Canada), and testing stocks helped inspire the SOPMOD stock and Magpul designs.

Compared with the M16A2, the Colt ACR had distinct furniture and features. It used a heat‑resistant handguard with venting and a front handstop, an elevated sight track with a white aiming stripe, a longer pistol grip, ambidextrous fire controls, a removable scope, and a six‑position telescoping stock. It also used a flash hider and a muzzle brake to reduce recoil, plus an oil spring buffer in the lower receiver to smooth the cyclic rate. All told, these changes cut felt recoil by about 40% compared with the M16A2.

A major and controversial part of the ACR was the “duplex” round idea: a single cartridge holding two projectiles. Olin Corporation tested three designs—two tungsten projectiles in a long-necked case, two 1.7‑gram tungsten bullets in a standard case, and a final design with two 5.7‑mm projectiles (about 2.3 g and 2.1 g). The last design was submitted for trials. The aim was to increase the number of projectiles fired, but the duplex rounds significantly reduced accuracy, limiting effective range. Users would still need traditional ammunition for longer-range shots, and the maximum effective range with duplex rounds was about 325 meters.

Key specifications
- Mass: 3.306 kg (7.29 lb) without magazine and sights
- Length: 1,031 mm (40.6 in) with stock extended; 933 mm (36.7 in) with stock retracted
- Cartridge: 5.56×45mm M855 or duplex rounds
- Action: Gas-operated, rotating bolt (direct impingement)
- Rate of fire: ~650 rounds per minute
- Muzzle velocity: 948 m/s (3,110 ft/s) with M855; 884 m/s (2,900 ft/s) with duplex
- Effective firing range: 325 m (duplex)
- Feed system: 30-round detachable box magazine
- Sights: 3.5x optic or interchangeable iron sights