The GG&G MAD (Multiple Aperture Device) BUIS (Back Up Iron Sight) was originally developed to fulfill a request from Naval Surface Warfare for a battle ready low profile back up iron sight that provided both a large and small aperture on the same plane and provide co-witness capability with the majority of red dot optics.The MAD has four apertures, two of each size (so that rotating the aperture disc in either direction will bring the next size into view). All apertures are on the same plane and are thus zeroed to the same point of impact. The aperture disc is knurled for easier manipulation in combat environments. The small aperture diameter is 0.073-inch and the large aperture is 0.199-inch in diameter. The standard military windage knob and windage screw are used. One click of the windage knob provides approximately 0.48 MOA change when mounted on the M16A2E4 rifle and about 0.65 MOA on the M4 carbine.The MAD mount body is CNC manufactured from billet 6061 T6 aluminum alloy and Type III hard coat anodized in a non-reflective black mil-spec finish to provide combat durability. The stem and aperture disc are made from solid billet 4140 steel and have hardened wear points for long service life. All steel components are black manganese phosphated per mil-spec. The MAD overhangs the rear of the receiver by 0.200-inch. This provides a lip so that the sight can be easily deployed even with a gloved hand. The sight stem locks in the up position with a positive mechanical detent system. Once placed in the up position, the sight cannot be folded down without depressing the spring assisted detent release button located on the left side of the sight base. This totally eliminates the possibility of accidentally lowering the sight.The MAD is the lowest profile BUIS with a locking detent and weighs in just over two ounces. It is now available with an option for Trijicon Tritium night sight inserts. The MAD is used by elite armed forces and law enforcement teams word wide. Don’t forget it is compatible with the AR10. Large aperture has two tritium night sight dots.