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Questions & Answers
I've seen this model listed as 1/3 MOA adjustments online. Is it 1/4 or 1/3? Expert Answer

This Trijicon TA31RCO-A4CP ACOG 4x32 USMC Rifle Combat Optical Sight features 2 clicks of adjustment per inch at 100 yards.

by Ethan, Gear Expert, March 30, 2023
How accurate is this scope with a full length barrel? An A2/AR-15A3 versus an M4gery? Expert Answer

Accuracy of the optic is not affected by barrel length. However, the bullet-drop markings may be off slightly with shorter barrel lengths as they are designed for the USMC standard M16A4 rifle which has a 20" barrel, using the standard military ammunition load. There are a number of ballistic calculators available that can help re-calculate those markings for a shorter barrel or different ammunition load.

by Carly R., Gear Expert, October 13, 2017
Customer Reviews
Helpful Positive Review Unquestionable Performance by JK, Verified Owner, January 31, 2024
Bought this for my M16A4 clone build, and it goes together like bread and butter. Ringing steel out to 500yds without a pause. The glass clarity and field of vision is un-paralleled and makes using the BDC really easy. The Eye-relief is the only issu...
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3/3 found this helpful
Helpful Positive Review Great Scope by RangeNovice90s, Verified Owner, April 11, 2024
- Arrived at my home in less than a week after ordering it - Was not as heavy as people on the internet claimed - Very clear glass, etched reticle definitely helps for those of us with astigmatism and weaker eyesight - Took it to the range to shoo...
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1/1 found this helpful
Helpful Positive Review USMC ACOG FOR 20 INCH by FAST EDDIE, Verified Owner, April 14, 2024
WHAT CAN YOU SAY ABOUT THE USMC ACOG IT IS AWESOME. THIS IS THE SAME ITEM ISSUED TO MARINES TO SIT ON THE M16-A4 IT IS COMBAT TESTED AND MARINE APPROVED I LOVE THIS SCOPE IT IS BUILT LIKE A TANK AND WORKS AWESOME.
1/1 found this helpful
Helpful Positive Review Handsome Scope by Bill, Verified Owner, March 31, 2025
Found this scope very easy to fix on target. It mounted well on the picany rail on my AR. I have not used it for distances even though it has a scale to target up to 800 meters.
1/1 found this helpful
Helpful Positive Review TA31 RCO for M16a4 by Ray, Verified Owner, March 4, 2022
This is the real deal mil spec ACOG used on the M16A4. It is designed to be used with a 20 inch barrel. Looks great on my FN A4 clone, I switched out the mount for the LARUE mil spec mount, I prefer the QD levers over the knobs. Crystal clear glass a...
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2/2 found this helpful
Helpful Positive Review jack walsh by Legacy Reviewer, Verified Owner, March 13, 2012
Two tours with this scope i'll never use anything else. Application specific optics may perform better for their specific tasks, however nothing will beat this lens in terms of overall performace. Pros: Durability, reticle luminosity, battery free C...
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12/12 found this helpful
Read All 29 Reviews

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Reticle: Illuminated Red TA31RCO-A4CP Chevron Reticle Focal Plane: Second Focal Plane (SFP) Illumination Color: Red Finish: Matte Color: Black Weight: 9.9 ozAdjustment Click Value: 0.25 MOAAdjustment Type: MOA Illumination Type: Fiber Optics , Tritium Included Accessories: TA51 Mount Condition: New

Code: TJ-RS-TA31RCO-A4CP-EE

MPN: TA31RCO-A4CP

UPC: 719307302068

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Product Info for Trijicon TA31RCO-A4CP ACOG 4x32 USMC Rifle Combat Optical Sight for A4 w/ TA51 Mount

Trijicon TA31RCO Rifle Scope is an Advanced Combat Optical Gunsight (ACOG) designed for the M16A4 weapon system (20" barrel). Trijicon TA31RCO-A4 ACOG 4x32 USMC Rifle Combat Optic for the A4 w/ TA51 Mount provides the shooter with quick target acquisition at close combat ranges while providing enhanced target identification and hit probability out to 800 meters utilizing the Bullet Drop Compensator. Trijicon TA31RCO-A4CP ACOG 4x32 Scope with BAC USMC Rifle Combat Optic (RCO) for A4 incorporates dual-illumination technology using a combination of fiber optics and self-luminous tritium. This allows the aiming point to be always 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. Trijicon TA31RCO A4CP 4 x 32mm ACOG Advanced Combat Optical Gunsights hit fast in any light. Trijicon ACOG 4 x 32 Rifle Scopes are internally-adjustable, compact telescopic sights with tritium illuminated reticle patterns for use in low light or at night. Trijicon 4x32 ACOGs combine traditional, precise distance marksmanship with close-in aiming speed. Although Trijicon ACOG 4 x 32 Rifle Scopes TA31RCO-A4CP have many features which are very advantageous for military use, they were developed by Trijicon without government funding. Designed for use with the M16 family, every feature of its mechanical and optical design was chosen for a single purpose: to provide increased hit potential in all lighting conditions - without failure-prone batteries.image

Specifications for Trijicon TA31RCO-A4CP ACOG 4x32 USMC Rifle Combat Optical Sight for A4 w/ TA51 Mount:

Manufacturer: Trijicon
Objective Lens Diameter: 32 mm
Magnification: 4 x
Reticle: Illuminated Red TA31RCO-A4CP Chevron
Reticle Focal Plane: Second Focal Plane (SFP)
Exit Pupil: 8 mm
Illumination Color: Red
Finish: Matte
Field of View, Linear: 36.8 ft at 100 yds
Field of View, Angle: 7 degrees
Eye Relief: 1.5 in
Color: Black
Weight: 9.9 oz
Adjustment Click Value: 0.25 MOA
Length: 5.8 in
Adjustment Type: MOA
Parallax: Fixed
Illumination Type: Fiber Optics, Tritium
Fabric/Material: Forged Aluminum
Shockproof: Yes
Fogproof: Yes
Package Type: Polymer Hard Case
Included Accessories: TA51 Mount
Magnification Type: Fixed
Condition: New
Housing/Frame Material: Forged Aluminum
Country of Origin: USA

Features of Trijicon TA31RCO-A4CP ACOG 4x32 USMC Rifle Combat Optical Sight for A4 w/ TA51 Mount:

  • 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.
  • Take Control: 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 Trijicon's Bindon Aiming Concept (BAC) feature allows for improved situational awareness.
  • Outstanding Clarity: The quality of the glass and multi-coated lenses maximize light-gathering capabilities and clear field of view with zero distortion.
  • Exact Target Distances & Holds: Most ACOG models feature a bullet drop compensating and target-ranging reticle for decisive aiming.
  • Combat Proven: No other magnified optic has been used more in combat than the ACOG.
  • Shock-Resistant: Proven to withstand recoil from a .22LR to a .50BMG and everything in between. Easily passes U.S. Military drop test requirements.
  • Waterproof: 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.

Package Contents:

  • Trijicon TA31RCO-A4CP ACOG 4x32 USMC Rifle Combat Optical Sight for A4 w/ TA51 Mount
  • 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

Trijicon TA31RCO-A4CP ACOG 4x32 USMC Rifle Combat Optical Sight for A4 w/ TA51 Mount Orderable Models

List of Orderable Models

Trijicon TA31RCO-A4CP ACOG 4x32 USMC Rifle Combat Optical Sight for the A4 w/ TA51 Mount Rifle Scope , MPN: TA31RCO-A4CP , UPC: 719307302068 , Code: TJ-RS-TA31RCO-A4CP-EE

Trijicon TA31RCO-A4CP ACOG 4x32 USMC Rifle Combat Optical Sight for A4 w/ TA51 Mount Unavailable & Discontinued Models

List of Unorderable Models

Demo, Trijicon TA31RCO-A4CP ACOG 4x32 USMC Rifle Combat Optical Sight for the A4 w/ TA51 Mount Rifle Scope , MPN: TA31RCO-A4CP-DEMO , Code: TJ-RS-TA31RCO-A4CP-DEMO
Trijicon TA31RCO-A4CP ACOG 4x32 USMC Rifle Combat Optical Sight for the A4 w/ TA51 Mount w/FREE Gerber Suspension Multi-Plier 1471 , MPN: TJ-RS-TA31RCO-A4-KIT2 , Code: TJ-RS-TA31RCO-A4CP-KIT2
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