The recessed chamber holds 100gr FFg, so the minimum is 100 just to be sure there is no gap between the ball and powder, as far as maximum goes, in theory you could load it to rifle charges but it would recoil enough to break a normal man and a huge amount of powder would be just blown out the front and wasted. I really don't know how high a guy could take it before it became injurious or even possibly dangerous, but the barrel and breech would handle about any charge you could fit in it and still seat a bullet on it.

I don't plan to find out either, I need my wrists so I can keep working on the Rifle.

Colin