I did the same thing with my son when he was 9. Tried 30 grains of Pyrodex "P" behind a .45 roundball - no problem. Went up to 50 grains. Still OK, but did not want to go higher. This year, he turned 12. Still only 110 pounds. I'm going to try a .50 348 grain Powerbelt with 75 grain of T7 FFF. If he can handle it, we are going elk hunting.