roundball or some all lead conicals would be a good place to start. The REAL conicals would fit that requirement just fine. I would start with 50 of them. After that use some JB bore polish and give the barrel a good going over. JB's will remove any nasty stuff in the bore of the barrel such as lead, etc. Then give it the cotton ball test if you have any doubts. See if it pulls fibers from a cotton ball when pushed through the barrel.

Good luck with your rifle....