I saw some peculiar looking scratching on the inside of some Lapua 308 necks recently and traced the problem to brass build up on my Lyman 30-Long M expander die. The stuff is really stubborn and I'm having a tough time removing it. So far I've worked on it pretty hard with steel wool which has gotten most of it off. Then I tried some Shooters Choice copper remover but that seemed like it did nothing. So just wonderinng if any others have experienced this and how they removed the brass residue?