The TA31RCO-M855 is an Advanced Combat Optical Gunsight (ACOG) designed for either the USMC M16A4 weapon system (20” barrel) or the M16M4 (14.5” 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 1000 meters utilizing the Bullet Drop Compensator. - No tools are needed for windage and elevation adjustments because the TA31RCO-M855 features external adjusters making it waterproof up to 11m without the caps. - The TA31RCO-M855 includes: - 1 Thumbscrew Mount (TA51) - 2 Assemblies 1/10 Miliradian External Adjusters - 2 External Adjuster Caps - 1 Lanyard Assembly for Adjuster Caps (TA71E) - 1 Scopecoat (TA96) - 1 LENSPEN® (TA56) - 1 RCO Manual - 1 Warranty Card - Magnification: 4x - Objective Size (mm): 32 - Bullet Drop Compensator: Yes - Length (in): 6.0 - Weight (oz): 14.2 - Illumination Source: Fiber Optics & Tritium - Reticle Pattern: Horseshoe w/Dot w/ Target Reference System - Day Reticle Color: Red - Night Reticle Color: Red - Calibration: 0.223 (14.5 or 20 in. barrel) - Bindon Aiming Concept: Yes - Eye Relief (in): 1.5 - Exit Pupil (mm): 8 - Field of View (Degrees): 7 - Field of View @ 100 yards (ft): 36.8 - Adjustment @ 100 yards (clicks/in): 2 - Mount Comes With: TA51 - Housing Material: Forged Aluminum