The GG&G A2 Style BUIS (Back Up Iron Sight) provides the operator with an easy-to-install and easy-to-operate flip up rear sight, and now includes an important new locking detent. 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 A2 BUIS can be used as a stand-alone sight or as a co-witness iron sight with most red dot sighting systems. When used with the M16/AR15/M4 Flat Top Co-Witnessing mounts for the L3/EOTech HOLOSight, the HOLO sight is positioned in front of the flip-up. The iron sight axis is typically positioned in the lower 25% of the HOLO sights heads-up display window.

This sight features the standard A2-style double peep aperture and has full windage adjustment. It uses the Colt-style windage knob and windage screw. 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. Initial zero is set by adjusting the weapons front sight post. The GG&G A2 BUIS is the lowest profile flip up iron sight with locking detent. When in the down position, it will clear most optics.