Trijicon ACOG (Advanced Combat Optical Gunsight) Optics

The 35-year history of Trijicon's revolutionary Advanced Combat Optical Gunsight (ACOG) optics continues.

November 09, 2022 By Tom Beckstrand

It’s not every day that any single gun-related product sees its 1,000,000th unit produced. Trijicon’s ACOG hit that benchmark back in 2017 — and it’s still running strong. There are 11 different ACOG models, and each has numerous options. However, it’s not just having relevant options that got this optic to where it is today. It’s easy to argue the ACOG is the world’s strongest and lightest combat optic ever produced, and here’s how that happened.

killFLASH by Tenebraex anti-reflextion device — “killFLASH” is a product developed by Tenebraex, which is used as an anti-reflextion device. Issued with military-issued Rifle Combat Optic (RCO) models, it can help to protect a soldier or Marine from revealing their position to a threat on the battlefield. (Mark Fingar photo)

Ruggedized Aluminum

In 1986, Glyn Bindon sat at his workbench examining a set of binoculars that had been disassembled. As he examined the eyepiece, prism and objective lens, he began to wonder if he could use a similar design to create a riflescope.

killFLASH by Tenebraex — (Mark Fingar photo)

Riflescopes at the time were large, complex, difficult to produce, and not especially durable. Riflescopes have many complex pieces, and Glyn figured he could eliminate one of the hardest-to-produce components, the erector assembly, and replace it with the roof prism found in many binoculars. Shortly after, the ACOG was born.

killFLASH by Tenebraex from below — (Mark Fingar photo)

Glyn’s son, Stephen, currently heads the brand. When he joined the company, there were three employees who worked from the Bindon home.

“This was the beginning of the black rifle heyday,” said Stephen Bindon. “While the ACOG was designed with the military in mind, it was designed to be the strongest and most compact optic possible.”

Trijicon developed wire-retained adjuster caps for an Israeli order in the late 1990s. The current configuration was the result of feedback from U.S. Marines in 2005. (Mark Fingar photo)

The ACOG consists of three optical components: The eyepiece, prism and the objective lens group. While the number of lenses in the eyepiece and objective lens group are similar to what is found in many riflescopes, the fact that those lenses are so close together required Glyn to use high-quality glass and a more sophisticated lens design — which involved cemented doublets, for example — to achieve the ACOG’s excellent image quality. The prism provided its own set of challenges, though, but Glyn worked through those issues to finalize the optical design that’s proven so successful.

long fiber optic for light transmission — The long fiber optic ensures maximum light transmission. Some cover it with duct tape and peel it back for a finer aiming point. (Mark Fingar photo)

Not only interested in simplifying the optical design, Glyn wanted to build the world’s most durable optic because he thought such an optic would be useful to the U.S. military. According to Stephen, “Dad made the optic as durable as the M16, and designed it to fit on the M16 carrying handle.”

From its earliest development, the ACOG’s durability was a top priority. As innovative as his optical design proved to be, the manufacturing of the optic was, and is, equally sophisticated.

The TA11 ACOG is a 3.5x35mm optic featuring superb field of view, magnification, and extended eye relief. The 3.5X ACOG has supported those in uniform since being chosen by U.S. Navy SEALs in 1991. (Mark Fingar photo)

Glyn started by selecting 7075 T6 aluminum and forged the ACOG housing. 7075 T6 is the most robust aluminum used in mass production, but it is expensive to form. It must be bought as billet or forged into shape since it cannot be easily extruded like 6061 optics. Few optic companies use 7075 T6 for any optic because of this. The only other optic company I know that uses 7075 T6 to construct the housing is Aimpoint. (Of course, Aimpoint also has an excellent service record with the U.S. military.) However, Aimpoint uses billet; Trijicon forges the ACOG housing. When it comes to impact resistance, forging makes the already durable 7075 even tougher.

Making the optic’s exterior as durable as possible was important to Glyn because he understood that the housing is the optic’s first line of defense. Optics rely on a precise lens arrangement to work effectively, so if the outside of the optic retains its shape, there’s a very good chance everything inside the optic will function as designed. There is no more durable an optic exterior than that found on an ACOG, which is part of the reason why it has been in service so successfully and for so long.

After starting with the most rugged housing possible, Trijicon cleans the flashing off the housing, which is created when the molds forge the housing into shape, and then a CNC-machine cuts the internal cavities. The two-step machining process ensures that internals are concentric and the distances between the lenses are exact. Limiting this process ensures minimal sample-to-sample variation and maximum optical quality.

Trijicon Specialized Lens Mounting — Trijicon’s specialized lens mounting method protects lenses against impact and breakage, while multiple coatings maintain clarity, even in harsh conditions.

The same processes that machines the exterior and interior of the housing also cuts the lens seats. Trijicon uses a unique method of mounting lenses that is only possible because of how they machine the ACOG housing. Most optics start off as a maintube that has lens groups contained within a unique housing. The lens group housing is then threaded into the maintube and secured. This approach creates a couple of mechanical issues that have to be addressed to ruggedize the optic.

The number one cause of a point-of-impact shift in any optic is lens movement. Smack a scope on the side and there’s a decent chance that the objective lens group will move .001 inch or more. That means the optic’s zero can shift an inch or more! A good optics company will pay a lot of attention to how the lenses get mounted in the maintube to ensure the lenses cannot move, no matter how hard the impact.

Trijicon doesn’t use the common construction method because there is no maintube. Trijicon cuts the lens seats directly into the forged housing to match the same radius as the lens it holds. Since the lens and seat are machined at the same angles, it’s impossible for one to move inside the other once the locking ring is in place. Even the locking ring has the same radius as the lens. Once the lens is sandwiched between the seat and locking ring, there is no way it can shift laterally or longitudinally because the lens dimensions would have to change.

Similar in size to a small red dot, the TA44 is a 1.5X optic that’s well-suited for compact, close-range firearms. The TA44 shown features an aftermarket LT105 ACOG compact mount from LaRue Tactical. $131 (Mark Fingar photo)

Once the locking ring is in place, it gets hit with a line of Loctite to ensure it can’t come loose. I can’t think of a more thorough way to secure lenses in position. The lenses in an ACOG will break before they move, and the 7075 T6 aluminum housing means that it is almost impossible for any of the lenses to break from an impact to the housing.

Glyn Bindon’s idea of simplifying the optical prescription is equally as brilliant as the mechanical and manufacturing process he developed to create the ACOG. It would have been sad to take such an efficient and innovative optical design and then use standard manufacturing techniques to create it. The way Trijicon makes the ACOG is every bit as important as the revolutionary prism concept that made it popular.

Base TA33 models include Trijicon’s removable TA60 thumbscrew mount for attaching the ACOG to Picatinny rails. (Mark Fingar photo)

Torture Tested

It’s easy enough to make the argument that the ACOG is the world’s toughest and most durable combat optic, but it’s always a good idea to consider supporting evidence. Here are some of the testing protocols that each ACOG must successfully negotiate:

Every ACOG must be able to survive a 61/2-foot (2-meter) drop to the ground while attached to a loaded M16A2 rifle or M4 carbine. The drop test occurs multiple times from various orientations. The weight of the M4 makes the direct drop onto the optic brutal, but the ACOG must remain functional to pass this test.

The next test is to put the ACOG on a recoil simulator and run it anywhere from 10,000 to 30,000 cycles on a hard-recoiling magnum rifle simulator. Trijicon is cagey and wouldn’t say what cartridge the recoil replicates, but it’s a cartridge that almost certainly no single human has fired 10,000 times!

Immersion tests are also on the menu. Trijicon immerses the ACOG to a depth of 66 feet and then leaves it for 30 minutes. No moisture is allowed to penetrate the optic. And the testing doesn’t stop there.

There’s some high-frequency vibration testing to see if anything comes loose, as well as high/low temperature operation testing to make sure everything works in the most extreme temperatures, per military climate standards.

Next, is temperature shock testing. The ACOG is run from really cold temperatures to really high temperatures to see if it still functions right. Finally, there’s chemical testing, salt/fog corrosion testing, and low-pressure testing for the times it rides in a cargo plane. All these tests look for a degradation in optical performance or fogging. The ACOG only passes if there is none.

I know of no other optic that is as thoroughly tested on a regular schedule for performance under such extreme conditions. It is for these reasons, combined with a few decades of strong combat performance, that I think the Trijicon ACOG is the world’s most durable optic.

Most ACOG models are battery-free and feature a tritium and fiber-optic illuminated reticle. Reticle brightness adjusts with ambient light. (Mark Fingar photo)

Pros & Cons

The ACOG would likely win a durability contest. However, while it is unlike any other optic, it’s only fair to assess the strengths and weaknesses of the design. ACOG strengths are its durability, simplicity, compactness and weight. The ACOG’s biggest weakness is that the customer has to know what optical qualities they’re looking for or they may select an ACOG model that doesn’t have the characteristics that they desire.

There are three optical qualities to consider when choosing an ACOG: Eye relief, field of view and magnification. Any prism design cannot bring a high quantity of each into a single optic.

Consider the most prolific combat optic of our time, the TA01, for example. It’s light, durable and compact. It has 4X magnification, great image quality, and a massive field of view. The only characteristic to consider is its short eye relief.

The TA01, in various configurations, has been issued by just about every branch of the U.S. armed forces since production began in 1987. It also requires the shooter’s face to be fairly close to the ocular lens. This isn’t a problem on a low-recoiling rifle such as the 5.56 NATO M16 or M4, but it might not be a great choice for the FN SCAR 17, a light 7.62mm rifle that recoils more.

I think the perfect ACOG for the SCAR 17 is the TA11, a 3.5X ACOG that has an additional inch of eye relief when compared to the TA01. It is larger than the 4X TA01 (and has a touch less magnification), but the TA11 has more eye relief that decreases the chances of the optic smacking you in the face during recoil, and it still has a huge field of view. For the small increase in size, it gains a lot of optical characteristics that make it better suited for heavy recoiling rifles.

The ACOGs that are my personal favorites are the TA44 and TA33. The TA44 came along in 1993 and is the most underappreciated ACOG, in my opinion. It is 1.5X, so it functions almost identically to a red-dot sight. However, it may be the most durable optic ever created. It’s tiny, takes no batteries, works in any lighting condition, and doesn’t care about the condition of the shooter’s eyes. Many aging shooters will acquire a degree of astigmatism, which makes the illuminated dot in a red-dot sight take on an odd appearance. Dots can appear as squiggly lines or smears, which makes it hard to achieve a precise point of aim. The TA44 doesn’t have this problem. The durability, size and utility of the TA44 make it one of my top two picks for use atop any AR-15 or other modern semiautomatic carbine.

The TA33 was added to the ACOG product line in 2007. It is my favorite ACOG for applications that require more magnification than 1.5X. The TA33 offers 3X, but it still features the smallest footprint possible. Like the TA44, it is a “mini ACOG” with a good amount of eye relief. The field of view is a bit tight, but the durability, small size and magnification make it a close second in the bid for my favorite ACOG.

Even after 35 years, Trijicon’s ACOG is unlike any optic currently available. While it has been imitated, few have demonstrated the originality and creativity that Glyn Bindon had. And no one else came up with such an innovative manufacturing process.

Glyn Bindon died too early from a plane crash in 2003. He didn’t see the widespread acceptance of the ACOG, first by the U.S. Marines in 2004. Even today, the ACOG has no competition in the low-powered combat optic category.