Get some 0.490 balls, and some pocket drill and bull denim from Joann's for patches. Use whichever one gives you the best groups that you can get into the bore. You might have to use a short starter, but the tighter the better as long as you can load it. If using real BP, get 3f and start at 70gr going up in 5gr increments. You might have to use a real hefty charge to get your best group with that slow twist. Use hoppes BP cleaner or spit as lube for practice and track of the wolf mink oil patch lube for hunting.
If you're using a tight ball and patch combo, and that barrel is like new, then you may need to smooth out the crown to prevent patch damage when loading. You can do that by using some 300 grit sandpaper wrapped around your thumb in a cone shape and twisting your thumb in the crown a bit, rotate the barrel 90° and do it again, repeat that until you've gone in a full 360. When there are no sharp edges on the crown perpendicular to the bore, then you should be able to load a tightball and patch without it cutting the patch.
