Dirt on reclaimed bullets isnt a whole lot differant then dirt off used wheel weights.
As mentioned all unwanted dirt, jackets, wheel weight clips float to the top and can be dipped out.
How every, before you start "dipping" flux the lead to mix up the additives you dont want "dipped" out.
ingots are best made outside if possible. Fill up the pot and fire it up, perferrably in the drive way or gravel, away from any combustable material and STAND BACK while the lead is being heated up, not only incase there is hidden moister, but I've seen dud rounds go off in a lead post.
Lots of times people will get a round, 22 or even reloads that didnt go off and they get tossed down range.
Nothing is more fun then having a round cook off in your lead pot.
Get it all set up, build the fire, then go set in the shade with a cup of coffee until the lead is totally ready to cast into ingots. Once its that hot, you dont have to worry about moisture or unfired rounds blowing hot lead all over the place.
Trust me, even a 22 round going off in a lead pot will teach you to dance.