The GG&G GS-1 FIRE System optical mounting rail was designed for mounting a conventional type scope on the AR/15/M16. It provides significantly longer eye relief for a proper scope/operator interface and the capability of attaching additional optical devices, such as a night vision monocular. The back of the rifle scope rail has been tapered to blend with the rear of the upper receiver and is not designed to mount a BUIS flip-up rear sight. It extends three inches over the hand guards and clears the M4 forearm. Manufactured from billet 6061 T6 aluminum alloy and Type III black hard-coat anodized, the GS-1 rail mounted scope meets MIL-STD-1913.