RE: slug rifle
I've heard great things about the Ithica's. The H&R's are great single shot slug guns...and they're cheap. I have a Rem 1100 that is a decent shooter.
If money is no object...look at a Tar-Hunt. I shot one this fall, and itwas a legit 200yd gun with Lightfield sabots and a quality scope..
I believe the gun I was shooting was 3" high at 100 and like 7" low at 200. Don't quote me on that, but it's close.
Just shoot every type of slug until you find one that groups...That's the key in a slug gun. I've seen smooth bores shoot great groups at 100yds and I've seen rifled barrels shoot 10" groups at 50yds off sand bags with a scope.
Good luck!