Trijicon TA31DOC ACOG Gunsight with Docter Optic Red Dot Sight


by Jeff Quinn

photography by Jeff Quinn

January 31st, 2006




Anyone who has watched the evening news pictures of our troops fighting in Iraq and Afghanistan have surely seen the Trijicon ACOG gunsight atop the M-16 and M-4 rifles carried by our elite fighting units of the US Army and Marine Corps. The ACOG has proven itself in battle to be an accurate, tough, durable, and reliable scope sight. These sights are the preferred equipment of the troops who can get their hands on one, and they are becoming more prevalent on the battlefield daily. I own two of the ACOGs, and have found them to be an ideal scope sight for AR-15 and AR-10 rifles that are set up for social work, and they can also serve well for hunting.

The ACOG is a very compact scope, and the reticles are calibrated for either 5.56mm or 7.62mm NATO cartridges out to 600 meters for some models and 800 meters for others. All ACOGs have tritium illumination for the aiming point of the reticle for operation in all lighting conditions, even complete darkness, without ever needing batteries. Some ACOGs also incorporate the Bindon Aiming Concept (BAC), which brightly illuminates the reticle in daylight for quick use with both eyes open.

The ACOG achieves its compactness from a prism arrangement, and uses a very heavy duty aluminum housing that can withstand a lot of abuse. While "tactical" and "mil-spec" are highly overused terms these days, they do apply to the ACOG. It is a serious piece of equipment for those whose lives depend upon their equipment working properly, every time.

While most ACOGs are of four power magnification, which can greatly increase the hit potential of the weapon at extended ranges, sometimes no magnification is better. For distances that are best measured in feet instead of yards or meters, a simple red dot with no magnification is quicker to use. Apparently, some Special Forces units were mounting red dot sights atop their ACOGs for use in house-to-house fighting, where getting a rifle into action quickly when clearing out a room is the task at hand.

Trijicon is now building an ACOG with a red dot sight from Docter Optics mounted on top. This red dot sight is not to be confused with the cheap junk that can be found at gun shows or in discount catalogs. The Docter Optics dot sight is also a serious and rugged piece of equipment. It is also built to withstand abuse. Its dot is powered by one readily available 2032 lithium battery, and subtends three and one-half minutes of angle. The sight is easily adjusted to point of aim by two screws. The Docter sight has no on/off switch, and it never turns completely off. However, the darker the environment, the dimmer the light becomes, as it should. The Docter has a plastic cover that puts the sight in "sleep" mode, simulating total darkness. In this mode, the light is so dim that Docter claims a battery life of four years in this mode.

The ACOG/Docter combo sight provides what is perhaps the ideal battle sight for all conditions. I tried the sight on an AR-15 chambered for the 5.56mm NATO cartridge, and also on my .50 Beowulf AR. This model of ACOG has the reticle with the BAC, and the center portion of the crosshair is illuminated at all times. It works very well in bright daylight and also in total darkness, in open fields and in deep hardwoods. In every condition in which I tried the ACOG, the center crosshair was visible. The reticle on this model is meant to be sighted in at 100 meters, and has aiming points marked at 100 meter intervals out to 600 meters, regulated for the current 5.56mm NATO cartridge. The Docter red dot I sighted in to be dead on at 40 yards, and its dot was visible also in all lighting conditions from bright daylight to total darkness, and everything in between.  I love the fact that both the ACOG and the Docter sight get dimmer as the light fades. Some lighted sights stay too bright in dim light, and practically blind the user to his surroundings. This sight does not have that flaw. The lighted crosshair and the dot are regulated to the existing conditions.

The reticle in the ACOG is similar to the one in this graphic:

The difference is that the graphic above shows the center crosshair lighted only at night. However, the ACOG examined here also has the BAC fiber optic unit that lights the reticle at all times. I attempted to get a picture of the reticle in use, but due to the limitations of my camera, it would not focus properly on the reticle, so I included the graphic from Trijiconís website. The reticle is very easy to use, and quick to get on target. There is no need to worry about holdover at extended ranges. As long as you know the distance, just hold on the proper aiming point, and press the trigger.

The new TA31DOC weighs just over  sixteen ounces, including the mount.  It is a tough, reliable, and very useful gunsight for any condition. It is perfect for a home defense rifle, and would also serve very well for hunting game animals from arms length to a couple of hundred yards.  Check out the prices and specifications on this and other Trijicon products online at:

The ACOG/Docter combo sight ainít cheap by any means, but when you need a quality sight for a serious purpose, it is worth the price. If it is good enough for the best military fighting units in the world, it is good enough for me. I highly recommend it.

Jeff Quinn


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Trijicon's TA31DOC ACOG Gunsight with Docter Optic Red Dot Sight.



Jeff considers the Trijicon TA31DOC perfect for both "Homeland Security" and hunting applications.





Fiber optic BAC allows the reticle to be illuminated at all times.



ACOG has precise but rugged adjustments.



TA31DOC has a mount to fit a "Flattop's" receiver rail.





Integrated Docter Optic Red Dot Sight allows for quick and accurate shooting when no magnification is necessary.



When not in use, covering the Docter sight puts it into "sleep mode".





Trijicon's TA31DOC ACOG Gunsight with Docter Optic Red Dot Sight - the ideal sight for a battle rifle.