My go-to recipe for most.58's is a .575 dead-soft ball and
022" denim patch. If that is a little snug as it was in my 1861
Enfield with what.574"bore, I drop to a little.562" ball and then.022"
denim patch and see how that shoots.
Since you mentioned 66" twist, I would likely test with the .575
.022 patch, water based lube for target testing, and start at 82 or 85gr.
of 2F GOEX, increasing the charge 5 gr. after each 5 shot group at 50yards.
I have found that nesting accuracy st 25yards is a waste of tome, powder and shot.
Keep US abridged omit your developments. You may wish to search for previous threads
on muzzle crowns if you.are cutting.patches at the muzzle when seating.them.