I do not need 9MM cases, if when I was sorting 10,000 9mm once fired cases I found cases with flat bottoms I would have rejected them, I want the bottom of my cases to have a cup shape above the web.
I would have measured the case head thickness looking for an advantage for unsupported case heads.
http://tincanbandit.blogspot.com/2014/01/kabooms.html
F. Guffey