10's are easy. Find the diameter of the bore first and foremost, then order the correct circle-fly wads. most sizes are available at trackofthewolf and other places.
: 27.3gr. = 1 dram
I'd start at 3 1/2 drams with 1 1/8oz to 1 1/4oz. shot for a good starting load.
A full power load for most shooting would run upwards of 4 drams and 1 1/2 oz.
You'll find some guys want to shoot modern-type loads (or heavier
in muzzleloading shotguns, but they aren't necessary nor advisable in my opinion.
Properly wadded, you will get excellent results with normal muzzleloading shotgun loads.
All that said, I'll edit to include a chart I forgot about. HA! Close enough.