Design
The ACOG is available in a variety of configurations from the manufacturer with different reticles, illumination, and other features. Most ACOGs 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 versions of the ACOG have an additional daytime reticle illumination via a passive external fiber optic light pipe. Normally this allows the brightness of the reticle to match the field of view since it collects ambient light from around the sight, although there can be a mismatch in lighting, such as sunlight hitting the light pipe directly. Reticles have other features such as a bullet drop compensator and other different reticle shapes such as chevrons.
Some ACOG models incorporate rudimentary ghost ring iron sights as a backup for targets that are within 50 m (55 yd). Most ACOG 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. Others include Docter or Trijicon reflex sights mounted on top. The ACOG ECOS line features both of these secondary sighting systems on the same scope.
Other features include Picatinny rails, flip caps, and the ability to be waterproof up to 11 m (36 ft).
Although the ACOG 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 later produced ACOG 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.
Read more about this topic: Advanced Combat Optical Gunsight
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