I was de-priming a batch of 9mm cases when the Lee (Guaranteed Unbreakable) universal de-capping die pin broke. The case that broke the pin looked like it was a dark colored brass. Inside it had two flash holes one on either side of the center, but none in the middle. The way it was made there was no way it could be de-primed with standard dies. The head stamp said 603, 9mm Luger and nothing else. The more I looked at the case the more it didn't look right. I finally tested it with a magnet and the case was steel. It looked like it had been coated with some kind of (almost) brass looking material. The finish was smooth and kind of slick feeling. Anyone know what it is?