Just a quick tip for the beginners; Casting really should involve two seperate and distinct melting operations if you are using mystery metal or scrap or even Wheel Weights.
1. Make ingots first - don't start casting bullets by dropping your scrap/scrounged lead into your actual bullet casting pot.
Instead, get or make yourself a larger cast iron dutch oven pot or cut a BBQ propane tank in half and use a turkey fryer propane burner to melt your scrap/scrounged lead in.
Take out all your floaters (clips, zinc, screws, rocks, and such) then flux a few times stirring and scraping the bottom and sides aggressively.
Scoop out the dross and ashes and such then pour your lead into approx 2lb ingots using whatever you can get. I like the older 1 piece muffin tins. I find them at yard sales or thrift stores (don't use modern muffin tins. They solder the cups to the flat part and your lead's heat just melts them and they come off.)
2. After you have a good pile of ingots, take those to your nice clean electric pot or a smaller pot over propane, and repeat the melting and fluxing. You will still get some "crap" in your melt that comes out when you flux but FAR LESS than if you start with your scrap/scrounged lead.
I made some pretty bad bullets my first time... someone set me straight with the above advice and I'm just passing it on.