I have no choice but to recommend a Simmons 7790D straight 4X scope with the Pro-Diamond reticle. (Yeah, blah, blah, blah it isn't a Leopold. Save it.) It is plenty of scope for slug distances. Nice crosshairs that are wide enough for the field and are finer in the diamond. Has great light gathering for dusk and dawn. And the Pro-Diamond is sweet. That diamond = 14" top to bottom at 40 yards so if you have an idea the size of a deer out there the diamond can act as a range finder.

I have (3) mounted on USHs and another on a Mossberg 500 slug gun. My oldest is on my 1997 12 gauge USH. NEVER had a problem at all with any of them.