The 'addiction' has begun!
A most beautiful rifle indeed.
The Pedersoli manual recommends using a .010 patch, a .490 round ball and 50 - 100 grains of powder with their .50 Kentucky.
And you'll find the rifles 'sweet spot' somewhere in between going up in 5grn. increments. IMO, the secret is consistency in the loading process. If you have a string of good shots, remember what you have done to obtain them.
Did you swab before each shot?
Did you tamp your powder(pouring powder down barrel and settling powder by hitting side of breech area with palm of your hand) between each shot?
How much seating pressure did you use?
Again, all about finding out what the rifle likes and repeating that loading process with consistency.
The biggest thing is to have fun !