I would suggest starting with 50 grains of the blackpowder of your choice, increasing the charge maybe 5 or 10 grains at a time until accuracy started to degrade, or you found the recoil knocked all the fun out of shooting the gun. Whatever comes first. Then back off 5 or 10 grains and call it a hunting load. Somewhere along the way you should have found your conical target load, though for a paper punching target load, I would consider trying a patched roundball.