GG&G 1005 A2 Flip-Up Sight The A2 BUIS is easy to install. When deployed in the up position, the sight cannot be folded down without depressing the spring assisted detent release button Can be used as a co-witness iron sight with most red dot sighting systems, as a stand-alone sight Made In USA Rear Sight features the standard military A2-style double peep aperture allowing for end user known point of impact.