You must use a buffer wad between the ball and the powder in order to prevent a chain fire. A chain fire occurs when the firing of one charge ignites all of the others. This could cause severe injury. An alternative to the buffer wad is to place a thick layer of grease over the ball. Both methods work well.
I choose to use the felt wad method, tends to be cleaner and faster. Cut your own from felt hats, felt pool table tops, any decent quality felt. Lubricate them using a decent lubrication, or good old fashion lard, not too much. Cut them with a large diameter hole punch, or such as you might find in a leather shop.
You can order the caps from Cabellas but probably better to find a local supplier.