ACOG Scope – Advanced Combat Optical Gunsight (ACOG) are a series of telescopic sights manufactured by Trijicon and designed to be used on the M16 rifle and M4 carbine. Models provide fixed power magnification levels from 1.5× to 6×. The ACOG scope is available in a variety of configurations from the manufacturer with different reticles, illumination, and other features. Most ACOG scope models do not use batteries for reticle illumination, being designed to use internal phosphor illumination provided by the radioactive decay of tritium. The tritium illumination has a usable life of 10–15 years. Some ACOG scope models have an additional daytime reticle illumination via a passive external fiber optic light pipe. Reticles have other features such as a bullet drop compensator and other different reticle shapes such as chevrons.
Most ACOG scope models, when mounted to a carry handle, have an open space through the mount to allow the use of the rifle’s iron sights without removing the scope. Some ACOG scope models include Docter or Trijicon reflex sights mounted on top. Some ACOG scope models incorporate rudimentary ghost ring iron sights as a backup for targets that are within 50 m (55 yd). The ACOG ECOS line features both of these secondary sighting systems on the same scope.
Other features of the ACOG scope include Picatinny rails, flip caps, and the ability to be waterproof up to 11 m (36 ft). Although the ACOG scope is designed for the Picatinny rail of the M16A4 and M4, with an adapter it can be mounted on the carrying handles of previous models. Trijicon has produced ACOG scope mounts and adapters for weapons besides the M16, including the Beretta AR70/90 series; SIG SG 550, Heckler & Koch, Bushmaster ACR, Enfield L85A2, and FN SCAR weapon systems; and the Steyr AUG.
Another consideration is to add night vision capabilities to the ACOG scope.