The bullets are not filling out because of the zinc. Take what ever lead you have melted to the scrap yard and get rid of it.
Now you are going to have to sort all of the WW. I use a large pair of side cutters. The zinc will not cut. Find a radio station you like and sit down and try to cut each one. You don't have to cut them in half. Just see if the cutter will cut into them. The zinc will feel like trying to cut a 1/2" bolt. It will hardly even scratch it. There is also iron WW. The zinc ones will be marked Zn, the Iron ones will be marked Fe. But not always. There is no way around this. This is all from the tree huggers.
