Advanced Combat Optical Gunsight Advanced Combat Optical Gunsights ( abbreviated ACOG ) are a series of telescopic sight s manufactured by Trijicon . The ACOG was originally designed to be used on the M16 rifle and M4 carbine , but Trijicon have also developed ACOG accessories for other firearms . Models provide fixed power magnification levels from 1 . 5× to 6× . ACOG reticle s are illuminated at night by an internal phosphor . Some versions have an additional daytime reticle illumination via a passive external fiber optic light pipe . Design . The ACOG is available in a variety of configurations from the manufacturer with different reticle s , 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 chevron s . Some ACOG models incorporate rudimentary ghost ring iron sight s as a backup for targets that are within . 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 sight s mounted on top . The ACOG ECOS line features both of these secondary sighting systems on the same scope . Other features include Picatinny rail s , flip caps , and the ability to be waterproof up to . 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 by using a special adapter . Trijicon later produced ACOG mounts and adapters for weapons besides the M16 , including the Beretta AR70 / 90 series ; SIG SG 550 , Heckler & Koch HK416 , Bushmaster ACR , Enfield L85A2 , and FN SCAR weapon systems ; and the Steyr AUG . Bindon aiming concept . Several ACOG models are designed to be used with the " " Bindon Aiming Concept " " , an aiming technique developed by Trijicon founder and optical designer Glyn Bindon . The technique is essentially using the illuminated part of the reticle and its focusing rear eyepiece as a collimator sight . As in any other collimator sight , the user does not actually look through the sight but instead keeps the collimated ( infinity ) image of the illuminated part of the reticle in focus with the dominant eye while the other eye views the entire field of view to acquire the target . In this both - eyes - open technique the brain superimposes the aiming reticle on the target . An added part of the technique is to shift focus after acquisition to the dominant eye / telescopic image for more accurate shooting . This overcomes the problem of centering or acquiring fast traversing targets common with all telescopic sights . Only certain models of the ACOG are designed with bright - enough daylight - lit fiber - optic or battery - powered LED reticles that facilitate this technique . Users . The United States Army , Air Force and Marine Corps field the Trijicon TA31RCO ACOG , a 4x magnification model with 32mm optics ( 4×32 ) , with specially designed ballistic compensating reticles that are fiber optic & tritium illuminated , for the M4 carbine and M16A4 rifle . This sight is designated the " M150 Rifle Combat Optic " in Army service and " AN / PVQ - 31 Rifle Combat Optic " in the Marine Corps . After an October 2005 evaluation , the USMC fielded 115 , 000 ACOGs so that every rifle and every carbine in the Marine Corps inventory would be equipped with one . The TA01NSN , a 4x32 ACOG with only tritium night illumination and backup iron sight s , is included the Special Operations Peculiar MODification ( SOPMOD ) kit for the M4A1 carbine used by Special Operations personnel to configure their weapons to individual preferences and mission requirements . Other Trijicon models have also seen service after being purchased at the unit and individual level . Controversy . Trijicon has been the subject of some criticism for inscribing a reference to a Bible verse address ( ) alongside the model numbers on their ACOG sights . Starting in late 2009 , Trijicon began shipping sights to the U . S . military without the Bible verse .