For whatever it might be worth I have shot round balls from a number of different calibers with success. .25, .30, .35 and .44. I like to paper patch my balls for the .44, otherwise it has been Alox lube for the smaller calibers. I shot some loads with the .44 that had two balls and you can probably shoot both your balls thru any caliber with a straight wall cartridge. Maybe you could shoot 3 in a long case like the .45-70 or .38-55 if you have three balls. Some folk use different lubes, it really doesn't matter much with MF loads. Load whatever you got and send your balls downrange I say.
Accuracy will be better than you might expect, particularly with slow twist barrels that are typical of straight wall chambered barrels. Little bit of common sense and a little powder will go a long way to providing precision far beyond what you might expect. It helps if your balls are truly round. Not all balls are created equal. Swagged balls from Hornady are round, but geeze if that doesn't make me squirm a little.
Best of luck,
D
