I have a burris FastFire III and really like it. I would combine it with the Burris Speed Bead mount and go. I got mine for $170 at Optics Planet a month ago, I see they are higher now. I also have a Bushnell TRS-25, which would work great also. This is a $100 optic, but comes set for a picatinny mount... Either will handle the recoil of a mag shotgun with no problem. I prefer the open style of the FF over the closed style of the TRS, but both have plenty of field of view, especially for a shotgun.