.58 cal. is well covered by many moulds in many slightly different close sizes, round ball and slugs as well as traditional minnie 'balls'. ie; .562, .570, 575, .580 - RB moulds - slug and minnie moulds from .575", .577", .580", .585".

Being a Pedersoli, it will probably shoot RB's best. I would use a .570" ball and .018" patch, or a .562" ball and .022" patch. Pistols usually don't shoot more than about 60gr. of powder and that will give a good charge. Pedersoli will tell you the max charge for the asking.