I have experienced the same problem and found that if you soak the area w/ Hoppes 9 and let it sit for an hour or two and then take a tooth brush and scrub it will remove most if not all of the brass markings. If not complete the first time, do it again and you will find that it will eventually clean up pretty good. If that becomes a chore for you, a piece of electric tape will cover the area and keep the brass from marking the area of the deflector. Good luck