Advanced Combat Optical Gunsight

Advanced Combat Optical Gunsights (abbreviated ACOG) are a series of telescopic sights manufactured by Trijicon. The ACOG is designed to be used on the M16 rifle and M4 carbine, but Trijicon has developed ACOG accessories for certain other firearms. Models provide fixed power magnification levels from 1.5x to 6x.^[1]

Unlike many reflex sights, the ACOG does not require battery power. The superimposed reticle, available in a variety of patterns and colors, is illuminated by an external fiber optic light-gathering rail when available light is plentiful and by an internal tritium lamp during low-light use.

The ACOG is available in a variety of configurations from the manufacturer with different reticles, illumination, and other features. The TA01NSN features 4xmagnification and a crosshair reticle with a bullet drop compensator that allows the operator to engage targets out to 600 m (2,000 ft) without adjustments. Its reticle glows amber in darkness. It also incorporates rudimentary ghost ring iron sights as a backup for targets that are within 50 m (160 ft), but it is only usable when mounted on the carrying handle. The TA31RCO has 4x magnification, no iron sights, and uses a red chevron reticle which automatically adjusts to the ambient light conditions and has a bullet drop compensator that allows engagements at up to 800 m (2,600 ft). The M150 adds flip caps and is waterproof up to 11 m (36 ft). All ACOGs do not use batteries and are designed to be usable in any lighting. Features on other ACOGs include Docter reflex sights mounted on top, Picatinny rails, and mounted Trijicon red dot sights.

Although the ACOG is designed for the Picatinny rail of the M16A4 and M4, it can be mounted on the carrying handles of previous models.

Trijicon later began producing ACOG mounts and adapters for weapons besides the M16, including the Beretta AR70/90 series; SIG SG 550, Heckler & Koch, Bushmaster ACR, and FN SCAR weapon systems; and the Steyr AUG