Red Chevron Reticle, Thumbscrew Mount, Tritium / Fiber Optics Illuminated.
The Scope That Changed Everything.
There's a reason the Trijicon ACOG® (Advanced Combat Optical Gunsight) is the official medium-distance engagement optic of the Marine Corps and U.S. Special Operations Forces.
The one that started it all.
The concept was simple; a durable scope with a reticle that illuminates in low-light and no-light situations—without requiring the use of batteries.
More than 30 years later, the original ACOG stands the test of time as one of our most popular items. Choose from many 4x32 options, including the Official Rifle Combat Optic (RCO) of the U.S. Marine Corps.
The TA31RCO is an Advanced Combat Optical Gunsight (ACOG) designed for the USMC's M16A4 weapon system (20” barrel). It incorporates dual illumination technology using a combination of fiber optics and self-luminous tritium. This allows the aiming point to always be illuminated without the use of batteries. The tritium illuminates the aiming point in total darkness, and the fiber optic self-adjusts reticle brightness during daylight according to ambient light conditions. This allows the operator to keep both eyes open while engaging targets and maintaining maximum situational awareness. Designed to the exact specifications of the United States Marine Corps, the unique reticle pattern provides quick target acquisition at close combat ranges while providing enhanced target identification and hit probability out to 800 meters utilizing the Bullet Drop Compensator. No tools are needed for windage and elevation adjustments because the TA31RCO features external adjusters, making it waterproof up to 11m without the caps. Mounting bosses are integrated into the housing by the eyepiece to allow the easy addition of a Trijicon RMR® (not included).
Always On, Always Ready
Most ACOG® models are battery free, featuring a tritium/fiber optic illuminated reticle that automatically adjusts the brightness based on available light.
Several ACOG models are designed with a user adjustable brightness setting powered by a single AA battery. The 3.5x35 LED and 4x32 LED models both offer six adjustable brightness settings.
Rugged, Reliable Housing Design
Fixed-power design allows for minimal moving parts to create a nearly indestructible sighting system.
"Both Eyes Open" Design
“Both eyes open” shooting using The Bindon Aiming Concept (BAC) allows for improved situational awareness.
The quality of the glass and multi-coated lenses maximize light-gathering capabilities and clear field of view with zero distortion.
Exact Target Distances & Hold
Most ACOG models feature a bullet drop compensating and target-ranging reticle for decisive aiming.
No other magnified optic has been used more in combat than the ACOG.
Proven to withstand recoil from a .22LR to a .50BMG and everything in between. Easily passes U.S. Military drop test requirements.
Exceptional waterproof performance that exceeds military standards. Dry nitrogen-filled to eliminate fogging. This optic is tested to withstand and perform in extreme cold and heat with dry-nitrogen filled housing that mitigates fogging.
15.8 oz. (447.92g)
Day Reticle Color
Night Reticle Color
Bullet Drop Compensating (BDC)
0.223 (20 in.barrel)
Bindon Aiming Concept (BAC)
Fibre Optics & Tritium
Fibre Optics & Tritium
1.5 in. (38.1mm)
0.32 in. (8.13mm)
Field of View (degrees)
Field of View (feet)
36.8 ft. @ 100 yds. (12.27m @ 100m)
Flattop Thumbscrew Mount (TA51)
- Thumbscrew Flattop Adapter (TA51)
- Thumb Screw (for mounting to carry handle) (TA53A)
- killFlash Anti-Reflection Device (TA91)
- Scopecoat (TA96)
- LENSPEN (TA56)
- Lanyard Assembly for Adjuster Caps (TA71E)
- Trijicon Logo Sticker (PR15)
- RCO Manual
- Warranty Card