As the other posts stated the round ball will do you well. But you can also try other projectiles. Hornady PA conicals should shoot nicely also and you won't have to mess with patches. And also like Cayugad said, you don't need a lot of powder. Get yourself a powder measure and use loose powder - like Pyrodex RS (I assume it is a caplock) or FFg black powder. Start at 70 gr and shoot a group. Then move up in 10 or even 5 gr increments until you get it shooting nice tight groups. You will know when you hit the rifle's sweet spot when the groups start to open up. Remember to swab between shots to keep fouling down and your shot to shot consistancy. A simple spit patch followed by a dry patch will work while at the range.
AND - don't forget to snap a couple caps on the nipple BEFORE you load your first charge/ball to make sure you get all the oil out of the breech.