I don't know about the brass but the aluminum case blazer 9mm I use primarily dosen't have any black spots on it. It is a dull copper on the bullet. It's quite hot and very clean. I went through 800 rounds one range trip and didn't need to clean the gun buy the looks of it. Then I blew 1 box of WWB and definatley needed a scub after. Won't be buying any more WWB if I've got a choice.