CD - Great write-up.
In case you haven't looked it up already, the "SmE" on the cartridges stood for: "Spitzgeschoss mit Eisern" which means spitzer bullet with iron (core). If you put a magnet to the bullet, it would stick.
I always thought it odd that with the need for tanks and machine guns, they'd found steel and iron to be readily available enough to use them for an expendable like ammunition...