Advanced Combat Optical Gunsight includes TA51 flattop adapter. Features dual illumination; Fiber optics provides daylight illumination and tritium illuminates reticle at night. Fixed power, compact design, built for use in bright to low/no light. Waterproofing to 328 feet. Both eyes open design. he chevron reticle is designed to be zeroed using the tip at 100 meters. The width of the chevron at the base is 5.53 MOA which is 19 in. at 300 meters. This allows range estimation for silhouette targets. Features dual illumination (Fiber optics provides daylight illumination and tritium illuminates reticle at night). The ranging reticle is calibrated for 5.56(.223 cal) flattop rifles out to 800 meters.