So I recently PCSed to Maryland and the nearest ranges either don't allow black powder at all, or require frangible ammo. I just bought a Colt 1872 Open Top which I have been itching to shoot and was wondering if it is possible to reload black powder pistol cartridges with frangible bullets. They don't have a lube groove so I would probably have to lube the chamber mouths like a cap and ball revolver, but is there any other reason they wouldn't work. Barring that is there something else I can cast bullets out of? Zinc maybe?

I've read for casting zinc, the mould must have never been used for any other metal.