Trijicon ACOG 4×32 USMC RCO A4 Superb Combat Optic

Description

This is the one the Marine Corps actually issued. The Trijicon ACOG 4×32 USMC RCO A4 is Trijicon TA31RCO-A4CP, the Rifle Combat Optic built to the USMC specification for the M16A4, with a red chevron reticle calibrated for .223 out of a 20 inch barrel. Everything about it exists because a procurement document asked for it.

What Makes an RCO Different From a Catalogue ACOG

Mechanically the prism is the familiar TA31: fixed 4x over a 32mm objective, forged aluminium, fibre optics and tritium with no battery. What the Rifle Combat Optic designation adds is a specific reticle drawn to a specific ballistic solution. The chevron apex is the zero reference, the widening body is the close range shape your eye catches, and the stadia below it are ranged for the exact load and barrel length the Corps issued.

The chevron itself is worth understanding if you have not used one. The tip is a fine aiming point you can hold on a small target at three hundred yards. The body widening below it gives you something substantial to find at speed. It is a deliberate compromise between a dot, which is fast and imprecise, and a crosshair, which is precise and slow, and it is the reason the Trijicon ACOG 4×32 USMC RCO A4 works as a general issue sight rather than a specialist one.

Red rather than green was also a specification decision. Red preserves more of a shooter dark adaptation between shots, which matters when the same rifle is used at night. Green reads brighter in daylight. Neither is objectively better and Trijicon sells the pattern both ways, but the issued optic is red.

Trijicon ACOG 4×32 USMC RCO A4 Specifications

The reticle on the Trijicon ACOG 4×32 USMC RCO A4 is drawn for a 20 inch barrel, which is the single most important line on the specification sheet for a civilian buyer. Trijicon publishes a separate M4 version of the RCO calibrated for a 14.5 inch barrel, and the two are not interchangeable. A 20 inch upper pushes a 55 grain bullet roughly 150 to 200 feet per second faster than a 14.5, and by four hundred yards that difference is measured in feet of drop rather than inches.

Everything else follows the standard ACOG pattern. Eye relief is 1.5 inches, exit pupil 0.32 inches, field of view 36.8 feet at 100 yards across seven degrees. The housing is forged aluminium in matte black and the TA51 flat top thumbscrew mount is included, which is what the A4 upper receiver rail expects.

• Trijicon model TA31RCO-A4CP, USMC Rifle Combat Optic
• Magnification and objective: fixed 4x32mm
• Reticle: red chevron BDC reticle
• Calibration: .223 from a 20 inch barrel
• Illumination: fiber optics and tritium, no batteries
• Bindon Aiming Concept: yes
• Eye relief: 1.5 in. Exit pupil: 0.32 in
• Field of view: 36.8 ft at 100 yards
• Mount: TA51 flat top thumbscrew adapter
• Housing: forged aluminium, matte black
• UPC 719307302068

Honest Notes on the Trijicon ACOG 4×32 USMC RCO A4

Buy the right barrel length version. This is the most common mistake made with RCOs, because the two variants look identical and the part numbers differ by a few characters. If your rifle has a 16 inch barrel, which describes most civilian AR builds, neither version is exactly right: the Trijicon ACOG 4×32 USMC RCO A4 will have you shooting slightly high at distance and the M4 version slightly low. It is correctable once you have confirmed the stadia on paper, but you should know before you order rather than after.

Eye relief is 1.5 inches and the eye box is tight. This catches everybody coming from a low power variable, and it is not a defect. The design trades forgiveness for repeatability: get the mount position right and build a consistent cheek weld, and the sight picture is identical every time you come up on the rifle. Expect to spend a range session getting there.

Reticle brightness is automatic and cannot be adjusted by hand. That is usually an advantage, since the fibre optic scales with ambient light and never washes out or blooms, but it works against you in one situation: standing in a dark room looking out at bright daylight, the fibre is reading the room rather than the scene and the chevron can be dimmer than you want. The battery illuminated LED ACOGs exist for exactly that complaint.

The last honest point is weight and money. An ACOG with its mount is a little over a pound and costs more than many complete uppers. A modern low power variable offers a true 1x and more reach for similar money. What it does not offer is a sealed prism with a service record measured in decades and a reticle that works with no power at all.

Every Trijicon ACOG 4×32 USMC RCO A4 we list is current Trijicon production in the factory carton with the TA51 mount, lens covers and warranty paperwork. MAG5 Firearms is a family run FFL dealer in Collegeville, Pennsylvania, and optics ship direct to your door with no transfer needed.

See more rifle optics at MAG5 Firearms, or check the Trijicon TA31RCO-A4CP specification sheet from the manufacturer.