TA31F Features: -Scope.-The acogs (Advanced combat optical gunsights) are internally adjustable compact telescopic sights with tritium illuminated reticle patterns for use in low light or at night.-Bindon aiming concept (bac) models feature bright daytime reticles using fiber optics which collect ambient light.-Conventional riflescopes offer only a tiny exit pupil, requiring careful eye positioning directly behind the eyepiece.-ACOG provides maximum eye latitude behind the scope for easier target acquisition.-Multi-coated lenses provide maximum optical performance.-Forged 7075-T6 aircraft aluminum alloy housing, precision machined to exacting tolerances and hard-anodized to match the upper and lower receiver of the M16 rifle.-Internally adjustable because only the prism housing moves, the ACOG is much more rugged than conventional designs.-Aerospace seals make the ACOG waterproof to Navy Seal depths.-Eye-friendly advantage.-Magnification: 4X.-Eye Relief: 1.5".-Exit Pupil: 8 mm.-Field of View: 7.0 degrees.-Field of view: 36.8 ft at 100 yds.-Adjustment: 3 clicks per inch at 100 yds.-Tritium Activity: 100 milliCuries in one source. Includes: -Includes flat top adapter (TA51). Dimensions: -Weight: 9.9 Oz.-Length: 5.8".