These guns are simple.
Use groove+ diameter ball and 3-1/2 drams FFg Goex powder, add powder until they shoot together, nothing mysterious.

That's just about 100 grains FFg
I'd likely be adding 10-15 grains a load till it made a group.
Don't be bothered if it doesn't print to the same elevation as the sights.

Can you show the front sight please?

It looks like the leaves all lay down, so I'll assume one of them is marked for 50yds.
Use it on a target at 50yds and see how it goes.

Shoot that thing John!