Trijicon ACOG TA01NSN Scope is an ACOG(Advanced Combat Optical Gunsite) 4x32 Scope w/ Yellow Center Illumination for the M4A1 and fits the AR15/M16 “flat-top” rifles. It includes the TA51 mount. Modifications to this Special Forces model include a back up iron sight configuration that includes an integral rear ghost ring aperture and a tritium glow-in-the-dark front sight(Yellow Center Illumination) for close-combat/back-up sighting, and includes Flat Top Adapter, Backup Iron Sights and Dust Cover. The Trijicon acog TA01NSN 4x32 Scope was designed specifically for the US Special Operations Command SOPMOD M4 Carbine. To meet their requirements, the reticle bullet drop compensator and range finding stadia lines are based on the trajectory of the 62 grain bullet from a 16 inch M4A1 barrel. The ACOG TA01NSN is a compact and ruggedly designed scope and a valuable addition to any rifle - comparable to optical sights issued to British and Canadian Armed Forces. The finest optical design, 100% U.S. made components and Mil-C-14806A multi-layer coated glass elements make the ACOG the ultimate telescopic sight. The black daytime reticle in the Trijicon Scope ACOG TA01NSN 4x32 glows red at night and in low light due to its tritium composition. Forged aircraft aluminum housings - the same material as the M16 receivers - are precision machined and hard anodized to match the finish of the M16. Unique to the Trijicon TA01NSN is its internal adjustment capability - only the prism housing moves - making this the most rugged scope available. The ACOG will withstand exposure to temperature extremes, salt spray, fog, fungus, humidity, sand, dust, shock vibration and a free fall drop onto a hard surface. Aerospace seals make the ACOG waterproof to depths greater than 500 feet. A hole through the M16 integral base permits use of the iron sights without removal of the scope. It can be attached to the carrying handle with one or two screws (2nd screw is optional). The user does not need to make any special adjustments between shots at different ranges. The ranging is already built into the reticle pattern (parallax free along its vertical axis). The width of the horizontal lines corresponds to the height of a 19 inch silhouette at that range.