Should be a .310 round ball. Not sure on the patch thickness though. As for powder, I'd be looking at FFFg or Pyrodex P (if percussion) and starting with about 15 or 20 grains. 40 would be a bit much IMHO.
Dixie Gun Works should have everything you need. Matter of fact, I'd use the load data listed for their squirrel rifle as a starting point.