Trijicon TA31F ACOG 4x32 Scope w/Illuminated Red Chevron Flattop .223-100215 Military-Grade Aluminum Alloy Housing Forged 7075-T6 aircraft aluminum alloy housing provides for a nearly indestructible sighting system Binding Aiming Concept (BAC) Trijicon ACOG models equipped with BAC allow use of the both-eyes-open aiming method along with scope magnification sighting for rapid target acquisition - in any light Longer Eye-Relief Maximum eye-relief for larger caliber rifles and large exit pupil for faster target acquisition Internally Adjustable Since only the prism housing moves, the ACOG is much more rugged than the conventional designs Trijicon Fiber Optics Automatically adjusts the brightest level and contrast of the reticle to available light conditions