Brass turning black?

Two answers #1. No, #2 Yes!

BP will discolor brass, period! And it will corrode it pretty fast too! Most BP cartridge shooters take a jug of water & soap mix to the range with them to drop thier empty hulls is. This will help kill the acids in BP fouling and stop corrossion. But they will still discolor a good bit.

When you get home, remove the brass from the jug and air dry it, then simply drop it in your tumbler with your favorite media and brass cleaner. They will polish right up!.

I use either Cabelas Case Polish or plain old Brasso in my media, both seem to work equally well. Expect a bit longer run time in the tumbler though!