Like stated above, there is only one caliber. I use a felt wonder wad, 35 g of FFF black powder, and 250g Buffalo Bullet. It's a tight fit, and the bullet seats right at the lip of the cylinder. If you don't use the felt wad but a little wonder lube after you seat the bullet, you can use about 40 grns.
I use these loads for hunting. I prefer using the wad based only on the mess factor. But both are very accurate and manageable loads.