On Target Review—Trijicon ACOG TA31F Scope

TA31F. Note Killflash Anti-Reflection Device at the front of the scope.
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TA31F. Note Killflash Anti-Reflection Device at the front of the scope.

In several short decades Trijicon has experienced a meteoric rise in prominence that its competitors can only dream of. Founded in 1981, Trijicon has become synonymous with excellence and reliability on the battlefield. The Trijicon website states that “No other magnified optic has been used more in combat than the ACOG.”

This fact alone has made it a “must have” item for AR enthusiasts.


The company was founded by South Africa native Glyn Bindon, who immigrated to the United States in the mid-1950s and shortly after, received a degree in aeronautical engineering from Parks College in St. Louis, Missouri.

Mr. Bindon’s first job out of school involved the development of a shock absorber for the tail hook of the Navy’s F-8U Crusader, allowing the jet to be used on an aircraft carrier. During the 1970s, he worked for Grumman Aerospace and designed a valve used aboard the lunar module. After a stint with the Ford Motor company, he visited his former homeland of South Africa and struck up an acquaintance with the developer of the Armson OEG gunsight.

Mr. Bindon began importing the sights and later developed his own line of tritium equipped iron “night” sights for handguns. He called his company Armson, Inc., but later changed the name to “Trijicon, Inc.”

The company was also known for developing the Bindon Aiming Concept (BAC) which merges fiber optic illumination and magnified optics. BAC essentially tackles an age-old challenge common to all telescopic sights–acquiring rapidly moving targets. This led directly to the creation of the Advanced Combat Optical Gunsight (ACOG) which combined robust design with an efficient fiber optics system.

With the Bindon Aiming Concept, the operator can use the ACOG with both eyes to acquire the target. To make the two-open-eyes system work, the scope utilizes brightly illuminated reticles. (In the case of the TA31F, the reticle is a fire engine red inverted Chevron).

The fiber optic technology gathers sunlight to illuminate the reticle quite vividly during the day. At night you’ve got radioactive tritium to do the job.

The ACOG has become the company’s most popular product line. Essentially it allows for quick aiming while still offering a magnified view for long distance targets. Useful in combat situations, the ACOG systems are also handy for hunters and in self defense scenarios.

The company’s customers include the Marine Corps, the Army, Special Operations Forces, and other Federal, and state and local law enforcement agencies. In recent times US Army combat units and the US Marine Corps have acquired the Model TA31F for use in Afghanistan and Iraq.

The Box in the Mail

Suffice to say, On Target’s editorial team was quite pleased to receive a Trijicon ACOG TA31F for product review. The black, miniature Pelican box encases the distinctive, aerodynamically inspired scope in foam. It’s both a practical and well-orchestrated marketing touch.

Why this particular model? This item is designed to capture the best of two worlds–long range marksmanship with close-in targeting.

So what did we like about this scope?

  • Rugged dependability for starters. Add to that first class optics and something waterproof to handle whatever the weatherman delivers.
  • Fixed magnification is also appealing because it means few moving parts and by definition, a scope that will weigh less than a variable optic.
  • Then there’s that crisp, illuminated reticle powered by Tritium at night and the red fiber optic cable by day. No batteries needed, just a slightly radioactive isotope.

One thing that we really appreciated about this scope was how dead simple it was to mount on a rifle. With other manufacturers, installing a scope correctly on a rifle can be a challenging project. However, Trijcons come ready to rock. So long as you have a Picatinny rail, or in the case of an AR, the original receiver handle, you’re set. Simply tighten the mounting screws and bingo, you’re in business.

That brings us to the next question—is the TA31F right for you? There are a whole slew of reticles available.

This is what you see when peering into the scope. The chevron is great for just just about everything except paper.

If you’re shooting at paper most of the time or, don’t plan to use it for low light situations, a crosshair type reticle is probably better.

We were hoping the TA31F would work well for Kokohead, where targets range from 50 yards to 455 yards. We wanted a scope that could seamlessly dial in to both those extremes.

Home on the Range

The inverted chevron reticle provided a great sight picture. Using some inexpensive 55 gr bullets we were able to smack a 4” wide steel plate hanging from 300 yards with little effort. The key was learning where to place the bright red inverted chevron on the target, in order to account for the bullet’s drop.

Then there’s the wind. The crater area is always buffeted by breezes and this made a great test bed for the sight. By tweaking the right hand screw (which adjusts the horizontal play) we were able to correct for the off shore wind and get consistent hits.

The next challenge was to try and hit the distant-most targets.

For that purpose we swapped out the 16″ upper piston job from Sig and affixed the TA31F on a Colt upper with a 20″ barrel. We did the obligatory sight-in at 50 and 100 yards. We then tipped the barrel at the most distant A-frame, which is perched in a tiny nook on the crater wall.

Hanging unceremoniously at 455 yards, are three steel plates. From left to right they get progressively smaller. So small that the “+” on the reticle’s BDC conceals the target. (We do not know how large they are. Some day we will measure them). We calibrated the shot using the 400 yard mark on the reticle and were able to nail two of the three plates consistently. (One of us had a spotting scope so we were able to verify hits).

The one criticism–eye relief could be better.

The point is not that we are great shots. I understand that marksmen with iron sights can hit targets past 500 yards. We are not those guys. We are average shooters. With excellent optics such as the Trijicon, even a mediocre shooter can hit a very small object at just under 500 yards with some regularity.

The TA31 series seems to be an optimal balance of magnification and size.
It’s compact and, the chevron style reticle is very precise for point shooting out to 500+ yards. It’s also large enough not to get lost in rapid fire scenario. (If you’re shooting at paper most of the time or don’t need it for low light situations, a crosshair type reticle is probably better).

Was the TA31F perfect? There was at least one “short coming”, that is short eye relief. We’re talking about 1.5 inches. (Trijicon clearly states this on their spec sheets).

Another detail to consider: The ACOG is remarkably parallax free on the vertical axis. (Head placement “up and down” isn’t an issue). However, head placement on the horizontal axis is something you should be conscious of. (It’s not parallax free “side to side”). Thus if you move your head left to right you’ll see the reticle move in relation to the target. To avoid this effect you’ll have to keep your head square with the center of the site. A good, consistent cheek weld is important.

Can you live with these idiosyncrasies? When it comes to optics there’s rarely a perfect solution. In the scheme of things Trijicon’s peccadilloes are minor.

I’m not sure I would want this particular model on a 7.62 rifle, given the 1.5″ eye relief, but recoil is clearly not an issue with the NATO 5.56 round.

A TA31F from Trijicon will give you a chance to reach and touch something at up to 500 yards or more. Do you have the chops to make it happen?

As alluded to earlier, this model is battle-tested. Short of an apocalypse, chances are you’re not going to be able to fully “road test” this scope.

Is it overkill for the average guy?

A lot of people buy Rolexes or Omega Submariners that can function down to 300 meters. Chances are these same guys will never take their fancy watches to the bottom of a swimming pool. Does that mean buying them was a mistake?


You most likely won’t get to evaluate your TA31F in a life or death, “Restrepo” scenario. (We sure hope not). That said, it’s nice to know that your scope is going to handle any kind of situation you find yourself in.

At the very least, the ACOG will enable you to push the limits of your skills and the capabilities of your rifle as far as you want to take them.

All photos by On-Target Hawaii Staff. 

Questions?  Comments?  Contact us at ontargethawaii@gmail.com

Rob Kay writes about firearms for Hawaii Reporter and is the author of How to Buy an AK-47.
Read more of Rob’s articles on OnTargetHawaii.com





  1. […] On Goal Scope Review—Trijicon TA31F Is it overkill for the average dude? A whole lot of men and women purchase Rolexes or Omega Submariners that can perform down to three hundred meters. Chances are these very same guys will never ever just take their fancy watches to the bottom of a swimming pool. Does that imply purchasing them was … Read through much more on Hawaii Reporter […]

  2. Some words for this spotting scope: durable, fast and easy to use, clear objective lens and awesome look. Though it is a bit pricey, it is well worth investing. I bet you will not be disappointed.

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