Here's some loads from the Hodgdon Data Manual #23.
2 drams( 55 gr.)FFg, 3/4 oz. shot= 992 fps. MV.
2 1/4 dr.(61 gr.)FFg, 7/8 oz.shot= 984 fps. MV.
2 1/2 dr.(69 gr.)FFg, 7/8 oz.shot= 1014 fps.MV.
You can add more shot, and probably increase powder charges, too, but patterns will probably suffer if you put more powder in the load, or even use FFFg powder instead of FFg.
Choose the size shot to match the size game you are hunting. I use #5 for pheasants, and larger birds. Smaller birds, I will use either #8, or #7 1/2 shot. If I were hunting turkey, I would try to work up the tightest pattern load using plated #5 shot, and hold range to 35 yard or less- preferably under 25 yds. Because pellet energy is lower with the lower velocities of BP loads, compared to what we are used to using Smokeless powder cartridges, Use at least 1 Size larger shot size for the same game you shoot with smokeless powder loads, and reduce the maximum range by 10 yards- more, if your smokeless powder shotgun is choked full and your BP gun is cylinder bore-- to get your killing patterns with a BP smooth bore.