You CAN shoot wheel weight roundball. They will be a little lighter then pure lead. Pure lead has a BHN of 5-6 and wheel weight can run from 11-15. Brinell Hardness Numbers will only indicate how much they projectile might have a depression from the rifling.
I used to shoot wheel weight ball. They loaded hard because they do not engage rifling the way lead does. And I would not hunt with them unless you want super penetration and little expansion. Compared to lead that is.