I have had good luck with conicals I've molded myself. They tend to be less accurate because they might get canted in the chamber as they're loaded.
If you own Pietta guns be careful. The plunger on their guns is usually milled out in a concave shape for round balls and I learned the hard way they mash conicals.
Ubertis usually have a plunger milled for conicals that work for both, but even some of them have a concave base on the plunger.
I've never used semi wadcutters in a cap'n'ball, so what your will do .... the only way to know is to test.
Use pure lead, not alloyed with antimony or anything. It needs to be softer than modern ammo.