ACOG 3 X 30 Scope Dual Illuminated Horseshoe/Dot .223 Ballistic Reticle Battery-Free illumination-most ACOG models feature a tritium/fiber optic illuminated reticle that automatically adjusts the brightness based on available light Length (inch): 6.1 inch. Rugged aluminum-alloy housingforged 7075-T6 aircraft-aluminum-alloy housing provides for a nearly indestructible sighting System Both eyes open design.The ACOG can be used as a CQB sight when Shooting both eyes open utilizing the bindon aiming concept