So a shotgun capable of 5" at 100 yards (pretty tough to find in a typical smoothbore) needs a 7x scope? Amazing...
My dedicated slug barrel shoots better than 5", but it has never had anything other than a 3x leupold on it...
A 2-7 seems sensible ...but I was not kidding about the 2.5X. I laugh like crazy when I see a 3-9 on a muzzleloader...hysterical!