I have started finding 9mm Luger cases that are steel, brass plated, and boxer primed; they look like the usual brass cases. They are headstamped KMD and the year (23 on mine). Fortunately they seem to rust quickly when exposed to rain or dew. I found them running a magnet over range brass to pick out the usual steel cases. The only benefit that comes to mind is a source of boxer-primed cases for people who wanted to try to reload steel cases. As long as 9mm brass cases are plentiful and free for the picking up I won't be trying to reload steel.