BP Moulds are generally made for pure lead. When you cast a bullet, the lead shrinks as it cools. Wheelweight lead will not shrink as much as pure lead, and bullets may be oversized because of that.

If you are using a minie style, they are supposed to be somewhat undersized, as the bullets expand into the rifling as they move down the barrel. They were developed so a soldier could keep loading as his rifle got more fowled in battle. Not the best situation for a one-shot hunting scenario.

I use conicals that engrave into the rifling at loading. They start a little hard, then slide fairly easily down the bore, but light to moderate pressure is required.

What is the rifling twist rate of your rifle? Are you using a minie bullet?