Welcome cnybrian. You've just entered the best and "most comfortable" muzzle loading forum around.

I'm a Leupold guy myself. Have VX-II's on three of my guns and would recommend them to anyone. Don't have a Rifleman model, but would assume they arepretty much standardLeupold quality, which is good.

Don't have any Nikon scopes, but do have two Nikon binoculars and they are great. I don't think you can go wrong with any of those, though I would suspect the SlugHunter would have heavier cross hairs than I would want.