Hmmm, let's see...3/8 equals .375". Most likely that he's using a stock, off-the-shelf, roundball mold and the most likely size would be for a .36 cal. On average those are .350 and weigh about 70 grains, if you are using pure lead, stuff like wheelweight lead would be a bit lighter.
Grain weight x Velocity squared then divided by 450240 = ft/lbs of energy
70 x 200 x 200 / 450240 = 6.22 ft/lbs of energy