The difference just means that a slightly different plug gauge would go the whole length.

Have you actually measured the diameter of each tube? Or slugged the bores?

You will need the particulars of each tube for the bullet diameter where lead & black powder are quite forgiving. Then fireform cases to each chamber. Then you can call the cartridge whatever you want within reason. Remember standardization didn't come along till WWI.

Serbus,

Raimey
rse