Advanced Combat Optical Gunsight

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TA31RCO variant of the ACOG which is designated as the M150 RCO in United States Army service

The Advanced Combat Optical Gunsight (ACOG) is a series of prismatic telescopic sights manufactured by Trijicon. The ACOG was originally designed to be used on the M16 rifle and M4 carbine, but Trijicon has also developed ACOG accessories for other firearms. Models provide fixed-power magnification levels from 1.25× to 6×.[1] ACOG reticles are illuminated at night by an internal tritium phosphor. Some versions have an additional daytime reticle illumination via a passive external fiberoptic light pipe or are LED-illuminated using a dry battery. The first ACOG model, known as the TA01, was released in 1987. [2]

Down-range ACOG sight picture


The first ACOG model, known as the TA01, was released in 1987.[3][4] In 1995, United States Special Operations Command selected the 4×32 TA01 as the official scope for the M4 carbine and purchased 12,000 units from Trijicon.[5] Between 2004 and 2005, the ACOG was selected as the official Rifle Combat Optic of the United States Marine Corps, prompting Trijicon to produce 100,000 units for the US Marines in the following 18 months.[5]


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,[6] 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.[7] 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 this can lead to a mismatch in lighting - such as sunlight hitting the light pipe directly, or standing in a shadow - causing the reticle to be much brighter or darker than the target.[8] 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.[citation needed] Others include Docter or Trijicon[9] reflex sights mounted on top.[10] The ACOG ECOS line features both of these secondary sighting systems on the same scope.

Other features include Picatinny rails,[11] flip caps, and the ability to be waterproof up to 11 m (36 ft).[12]

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.[13] 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.[citation needed]

Bindon aiming concept[edit]

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.[14] 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.


Trijicon has been the subject of some criticism for inscribing a reference to a Bible verse (JN8:12, referring to John 8:12, "I am the Light of the World") 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.[15]



See also[edit]

  • Sight (device)
  • SUSAT, British 4× telescopic sight with tritium-powered illumination similar to the ACOG


  1. ^ "Official Listing of ACOG models". Archived from the original on 2011-02-04. Retrieved 2011-02-11.
  2. ^ "Acog History". Trijicon
  3. ^ "TA01 ACOG - Trijicon, Inc". 13 September 2011. Archived from the original on 13 September 2011.
  4. ^ "Trijicon 24 Days of ACOG Sweepstakes". Archived from the original on 22 September 2017. Retrieved 29 December 2018.
  5. ^ a b "Trijicon History". 5 May 2021.
  6. ^ - Oct 2011, Trijicon came out with a conventional battery-powered illumination ACOG [1]
  7. ^ Tritium has a half-life of 12.5 years
  8. ^ "Tactical Handyman – ACOG Fiber Optic Fix". 16 March 2010.
  9. ^ "TA648TRD: 6x48 Trijicon ACOG". Archived from the original on 2010-01-03. Retrieved 2010-05-23.
  10. ^ "TA01NSN-DOC: 4x32 Trijicon ACOG with 7.0 MOA Docter Optic". Archived from the original on 2010-01-03. Retrieved 2010-05-23.
  11. ^ "TA648MGO: 6x48 Trijicon ACOG with Red Chevron Reticle and Accessory M1913 Rail". Archived from the original on 2010-06-08. Retrieved 2010-05-23.
  12. ^ "TA31RCO-M150CP: 4x32 Trijicon ACOG Army Rifle Combat Optic (RCO)". Archived from the original on 2010-06-08. Retrieved 2010-05-23.
  13. ^ "FM 3-22.9 Chapter 2". 20 July 2011. Archived from the original on 20 July 2011.
  14. ^ Jane's international defense review: IDR., Volume 34, Issues 1-6
  15. ^ "Michigan Weapons Company Trijicon takes flak over soldiers' rifle scopes branded with Bible verses". New York Daily News. 2010-01-19. Archived from the original on 12 February 2019.
  16. ^,7340,L-3838264,00.html. {{cite web}}: Missing or empty |title= (help)
  17. ^ Vining, Miles (22 April 2016). "ISAF armament of BLS". Archived from the original on 20 August 2018. Retrieved 14 September 2018.
  18. ^ "Individual Weapons Replacement | Ministry of Defence Website". Retrieved 2021-02-02.
  19. ^ "Spanish Army procures the MG4 E". Heckler & Koch. 2007-08-02. Retrieved 2009-05-02.
  20. ^ "Kit Magazine, Issue 62 Winter 2007" (PDF). Ministry of Defence. Archived from the original (PDF) on October 1, 2008. Retrieved 2008-03-16. This technology is here now! So if you see strange-looking SA80s being carried by strange-looking men, then rest assured, those users that had the requirement, had the make-over, at a price.
  21. ^ "Trijcon TA31RCO-M4CP Rifle Combat Optic Review - Combat Optics Reviews".
  22. ^ "Trijicon website". Archived from the original on 2010-05-21. Retrieved 2010-05-23.
  23. ^ "Picatinny hosts 2008 Type Classification and Materiel Release Awards Ceremony". Archived from the original on 2010-04-01. Retrieved 2010-05-23.
  24. ^ "Quantico Sentry - Marines test combat optics curriculum". 2005-10-27. Archived from the original on 2011-07-25. Retrieved 2010-05-23.
  25. ^ Sweeney, Patrick (2012). Gun Digest Book of the AR-15. Vol. IV. Iola, WI: F+W Media. pp. 232–233. ISBN 978-1-4402-2876-6.
  26. ^ M27 First Impressions Archived 2013-05-08 at the Wayback Machine -, 20 April 2013

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