At the temps involved in bullet casting, 650-750 deg, the amount of fumes is very, very small. Good ventilation in your casting area is plenty adequate. It's much more important to wash your hands after handling lead. It's not absorbed thru the skin, but it's easy to transfer to your mouth, nose, food, etc.
You can learn all you want about bullet casting at
http://www.castboolits.gunloads.com/.
John