May want to start lower than 80. My 56 likes 70gr. real well with shot, and shoots best with 70, or 80. They shoot the same. Every barrel is different. I have used .53, .535, and .562 in my .56 and the .535 shoots the best whether with patch or just with a wad. Patched it shoots as good as I can off hand at 50yds. For the .58 I think I would try a .562, .570, and .575 and see how they do. You will need some different thickness of patch material. Shot I would use about an ounce, over powder wad, the shot, and another wad. My wads are wool felt. Have fun playing with it, just pay attention to what you are loading so you can replicate loads that work the best!