The pistol is a .44 caliber gun so it should be using .429 or .433 diameter lead balls patched with some cotton or linen material. The .010" thick patches will work.
The powder load for this little gun should be around 10 to 15 grains. You can use either real black powder, Pyrodex or 777.
If you don't have a powder measure, an empty .380 auto cartridge case will measure out 10 grains or, you can use 2, .22 longrifle cases worth of powder for 10 grains or 3 cases worth for 15 grains.
After shooting the gun, don't forget to clean it.
All of the synthetic muzzleloading powders and real black powder form corrosive salts (fouling) when they are shot and these will attract moisture that will rust the bore of your gun.
To clean your gun, use some soap and water. That will dissolve the fouling and wash it away. Don't forget to oil all of the steel parts after cleaning.