As idiotic as it sounds, once we passed the law up here in good old western NY to hunt with handguns back in the very early 80's, I never carried, or hunted with a slug gun again.
That was the hunter side of me, but the caster & hand loader side of me still continued on and obsessed over making a great accurate load for a shotgun. Part of the quagmire back then was that rifled barrels for slugs weren't commercially available......it was all smooth bores. I have several smooth bore (Foster type) slug molds and tried just about everything you can think of. I eventually dropped the quest and continued on with other ventures.......
That was until the advent of rifled barrels.........Not wanting to feel defeated on that quest, I resurrected it and finally found a load using the Lyman 525 gr. Sabot mold with a Winchester AA wad that would shoot & group right along with the best commercial sabots, if not better.
Btw......I had a JC Higgins back in the day that I did a lot of slug work with (that this post reminded me of). The one thing I found was that if I could get the slug to match the bore as close as possible right up front, it shot the best. Yes, I know the slug obturates on firing, filling the bore, but if I swaged the slugs first, they printed far better........usually the best I ever got in doing so at 100 yds. was about a 4" group with 3 out of 5 printing very close.
The type of powder made a major difference in many cases...........
Bob