On the photo of your case neck it shows both horizontal as well as vertical abrasion markings on the case neck. I am assuming the horizontal markings are from neck turning and the vertical is what you are expressing concern over. I have experienced somewhat of the same phenomenon. These "striations", if you will, have only appeared on brass sized with Redding "Nitride" bushings. I have Redding Nitride, Wilson "steel" and Whidden "steel" bushings. Why they have only appeared on the Nitride bushings escapes me. Having said that, I use the "Montana Extreme" nylon brushes and I take a drill and spin those brushes inside the bushing. Then I "wipe them clean" with a Q-Tip and old rag I use to wipe lube off of cases. Once the inside diameter of the Nitride bushings are cleaned and somewhat "lubed", I start using them again. I can go several hundred rounds before that "process" needs to be re-used.. Apparently, the introduction of the Nitride on the bushings, instead of increasing their lubricity, evidently contracts some debris that causes those striations. That debris, whatever it is, can be removed using the method I described above. It does work for some time>>>>although I am in the process of changing all my bushing over to either Wilson or Whidden.. There is less trouble.. I hope this helps..