The TA31USN-M855 is an Advanced Combat Optical Gunsight (ACOG) designed for either the 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. – 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 TA31USN-M855 features external adjusters making it waterproof up to 11m without the caps. – The TA31RCO-M855 includes: – 1 LaRue Tactical Mount (LT799) – 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: LT799 – Housing Material: Forged Aluminum