The TA31RCO is an Advanced Combat Optical Gunsight (ACOG) designed for the M4 and M4A1 weapon system (14.5" barrel). It incorporates 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. 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. Mounting bosses are integrated into the housing by the eyepiece to allow the easy addition of a Trijicon RMR. Includes a thumbscrew flattop adaptor, thumb screw (for mounting to carry handle), killFlash Anti-Reflection device, Scopecoat, LENSPEN, lanyard assembly for adjuster caps, Trijicon logo sticker, RCO manual and warranty card.