I am no expert on pressures, etc but most percussion pistols were designed to fire a round ball or a "historically correct" conical that had a long tapered nose and a very short driving band- the point being that there wasn't a whole lot of obduration(sic?) required for the projectile to enter the bore. Hard alloy lead with long driving bands- theoretically it ought to increase pressure, maybe increase it a lot.
A lot of local gun shows will have some local chap selling bullets he cast. I had one guy that must have bought bulk lead because he could cast them and sell them for less than I could do myself. I asked him if I supplied a mold- could he cast some special bullets. "Not a problem" says he, this guy bought the mold himself just to have it.
Look around for a guy like that, make sure it is pure lead.
Casting your own- I use a Coleman stove outdoors, a Lee mold, ashort stick, a dipper and a pot and a towel to toss the cast bullets. Simple operation.