Once you have cases that are suitable for loading, get a realistic powder charge in there and see how much room you have.
I haven't run into a case where there's room to waste with a fiber wad. The felt holds necessary black powder lube, and under pressure of burning powder the felt wad helps as a gas seal.

Again I typically run a ring or donut shaped felt wad under the ball. All wadding fully impregnated with black powder lube.

Cheers
Tinker