With a compression die I loaded 56 grains of swiss under a 337gr custom bullet @ .461 dia of my own design that I cast from a Lee custom bullet 6 cavity mold using a soft lead @1% tin. This gun was chambered for the Spencer 56-46 XL I would presume by Christian Spencer in around 1866-68. This load has been cornagraghed at 1322fps with a spread of 18fps. from this gun.
I do load some nitro powder loads for this gun in H4198 and A-1680 that run about the same velocity + or - around 25fps.
For those who might feel their pants trying to twist up at the mention of nitro powders, I'm on my 4 brick of primers now loading for this gun most of which have been nitro loads. I don't recommend that you do it but I probably will. Now to find a bigger buck.