The TA31RCO is an Advanced Combat Optical Gunsight (ACOG) designed for the M16A4 weapon system (20' barrel). It 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. The TA31RCO 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. Designed to the exact specifications of the United States Marine Corp, the unique reticle pattern 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.