Here’s How ACOG Scopes Work

The ACOG scope is one of the most famous sights in the world, with Trijicon’s beloved scope being relied upon by millions of shooters everywhere. Originally designed for the M16 rifle, this impressive scope has since evolved over time to become compatible with a wide-range of popular firearms, including the famous AR-15. With a diverse range of magnification, ACOG scopes are reliable at both close and medium ranges, and usually come with an illuminated interior that makes them ideal even for night-time shooting.

What’s in an ACOG scope, anyway, and how do they work? Here’s everything you need to know about what’s perhaps the most popular gun sight around, and why it’s so brilliant at guiding you to your target.

how acog works

The Advanced Combat Optical Gunsight

The Advanced Combat Optical Gunsight, or ACOG scope, has been proudly produced by Trijicon since they first released a model in 1987. Since then, the company has only expanded its offerings, and gunowners in this day and age can buy ACOG scopes in a line of optics that vary in size, magnification, and bulk. Virtually all ACOG options range from 1.5x to 6x magnification but come with fixed magnification. This means that while you can find options ranging from 1.5 to 6x, the scope you eventually purchase will only have that fixed magnification and will not be adjustable.  While ACOG sights are usually preferred by shooters roaming in the great outdoors, they can still be used in indoor ranges, too, especially if they’re at the lower end of magnification.

Some gunowners dislike the fact that ACOG scopes aren’t adjustable, but in reality, this means that there are fewer moving parts and that the scope itself is immensely durable. As a matter of fact, ACOG scopes are so rugged that many soldiers in the U.S. military famously use them when serving, come home, and pick one up for civilian use, having found them to be of military-grade quality and thus uber reliable. These scopes are also quite compact, and the simple red dot aiming reticle is a classic fixture.

How ACOG Scopes Are Powered 

Some ACOG scopes are powered by a battery, but one of the reasons that ACOG scopes became so famous in the first place is that many more are powered by a mixture of tritium and fiber optics. Tritium is an unstable radionuclide, meaning it’s radioactively decaying, but this doesn’t mean it’s dangerous or that it will mutate you into some hideous creature. As a matter of fact, this harmless radioactive decay is important because it emits energy that forces the phosphor in your scope’s reticle to glow. In plain English, this means that your scope is constantly illuminated with the help of radioactive science, helping you peer downrange even in dark conditions. The experts at Trijicon really know their stuff!

The fact that ACOG scopes rely upon the power of radiation isn’t just a neat bit of trivia, it also means that you don’t have to worry about lugging a battery around. This means you don’t have to shell out extra bucks for a replacement battery, tote around the extra weight that such a battery entails and worry about your scope suddenly malfunctioning because of wet conditions or inclement weather. If ACOG scopes are famous for anything, it’s that they’re immensely durable and built to last.

ACOG Scope Durability

Similarly, given that ACOG scopes are forged from high-strength aircraft aluminum, they can take quite a beating. Trijicon claims that ACOG scopes are essentially indestructible, and who could blame them? You could take a hammer to most of these scopes and still walk away with a functioning sight that can guide your bullets to where they need to be.


ACOG scopes are also famously waterproof up to 100 meters, with the United States military often equipping troops in the field with them to ensure maximum war-fighting capability. You don’t have to turn it on, zero in your sights, or worry about distance thanks to its bullet-drop-compensated reticle. All you have to worry about is shooting, which is any gun owner’s dream.

Versatility of ACOG Scopes

You may think that the ACOG is a scope suited for war, and it is, but that doesn’t mean it’s incapable of being used in times of peace. Another reason that ACOG scopes are so immensely popular is that they’re incredibly versatile, with amateur shooters, former veterans, and professional competition shooters alike all relying upon various ACOG styles. The U.S. Army Advanced Combat Rifle Program found that ACOG scopes were a useful addition to their operations in 1987, but Trijicon has issued new variations that are tailored for civilian and competitive shooters, too. While many marines who took part in Operation Desert Storm can regal you with tales of their ACOG scopes working in harsh conditions, many civilian hunters and competition shooters can also attest to their impressive durability.

These products are so popular that, in 2017, Trijicon celebrated the one millionth ACOG scope sold. While some have freaked out over the inclusion of tritium in ACOG scopes, the element is entirely harmless and won’t hurt you in any way. As the company’s website makes quite clear, Tritium is simply a radioactive isotope of hydrogen and is and odorless, tasteless, and colorless gas that interacts with your body just as hydrogen does. In other words, it’s totally harmless and you don’t have to fret about your scope being powered with the help of radiation.

How Long Will An ACOG Scope Last?

Over time, however, ACOG scopes can see their famous luster diminish as the laws of radioactivity take hold. ACOG scopes are supplied with 100 millicuries of tritium, which has a half-life of 12.5 years. After 12.5 years, then, the tritium in your ACOG scope will have decayed down to 50 millicuries, meaning your scope will be less luminescent than it was when you initially purchased it. This pattern will continue to hold true over time, too, meaning that in another 12.5 years your scope will possess only 25 millicuries, and thus continue to dim. Given that the half life of tritium is so long, most customers see little to no issue with this, as few shooters use the same scope for well-over a decade. In the short term, you never have to worry about your ACOG scope losing its luster or kicking out on you halfway through a day at the range.

How ACOG Scopes Are Used

Hunters who need to rapidly adjust the range at which they’re shooting may find ACOG scopes to be a hassle, given that they have a fixed magnification, but nearly every other group of shooters can find one way or another of making good use of an ACOG scope. Trijicon’s classic ACOG models still remain the best option for gunowners looking to pick up a new scope, so don’t be afraid to head directly to the manufacturer when seeking out a reliable source for your ACOG scope. The price may seem high compared to other similar scopes, but it’s important to establish that no style of scope is as broadly recognized for its durability and usefulness as ACOG scopes are.

From the United States military to domestic law enforcement officials and shooting enthusiasts, the ACOG scope has made a home for itself in American gun culture. Powered by radioactive decay and nigh-unparalleled in rugged durability, your average ACOG scope is any true marksman’s delight.

If you’re interested in seeing our picks for the best ACOG scopes, make sure to check out our post about the best ACOG scopes for AR rifles.