As you know brass is not easy to get, esp 223. So I purchased 500 once-fired military 5.56 to work up, and when it was time to clean I had a challenge because it was very tarnished and dirty. I have found Flitz Metal Polish to do a great job removing rust and shining metal in general, so I added a few "globs" totaling around 1 inch in length to the walnut hull tumbling media. Initially these formed media-blobs, but soon these dispersed. In short, after 4-hr tumbling the cankered cases were transformed into the brightest shining brass I have seen so far! It also cleaned the inside as far into the case as I could see, and surprisingly polished most of the primer pockets as well (some get impacted with the media and therefore not tumbled). Looks like the brass was hand-polished with Flitz!