I bought a military muckabouts one, utter utter ****, crap welling, bits of polymer stuck on it, crap paint job and didn't fit in the mount.
I bought a Crossfire one, different class, utter utter work of art for the money, all metal, all nicely welded, power coated, removable barrel (.50) and it went straight into the mount and even at the later optic mount fitted.
Do not MUCK ABOUT, Crossfire all the way!!!!!