3 3/4 drams seems to be the regulated charge. That is mild indeed. One would hope it will shoot something more as it's trajectory will be like a musket - dismal at best.
: A 9 dram charge (245.7gr.) will not make 1,800fps with a 10 bore round ball, let alone a conical. I know this from chronographing my 14 bore, which gave only 1,770fps with it's .684", 484gr. ball. I do not believe a 10 bore will make 1,800fps without smokeless, and even then, not within regulation.