RE: best slug guns
I did some research, and it seems Ithaca is not in buisiness any more. They did make a Deerslayer model made especially for slug shooting though. The deer slayer II and III have screwed in barrels and drilled and tapped recievers for optics. Also with a 1 and 28 inch twist rate for the barrel.
If you could find one of these it would fit your bill nicely I am sure. The down side is they are heavy, just as heavy as the H&R ultra, around 11 or 12 lbs! And they are expensive. From what I read the suggested retail price was close to a grand. I would think you get a tar hunt for that. You could get a couple H&R ultras with really nice scopes for that. Or a savage 210 with really great optics.
Browning also makes the BPS in a slug gun only set up wiht a cantilever barrel with a 1 and 28 inch twist. Nice guns, I have held one, but never shot one.
Paul