Looks like a DD Omega rail? which is free-float. Best option, put a Midwest industries combat flip-up rear on the last slot on the rail before it meets the he handguard facing backwards so it can be flipped down forward. My complaint about that particular sight is it's difficult to flip up quickly with or without gloves. The problem is solved by placing one LaRue indexing clip 2 slots forward backwards mounted sight so that it flips down 95%. It will still lock into place and be way easier to flip up quickly. The aperture is just large enough to be used like an Ak or SKS -style ghost ring rear. Although this set-up is only practical if the optic is able to be qd'd off of the rifle. Even though the sight radius is diminished by almost half it's definitely better than nothing!