Any one heard of or used PMC primers?

[Bill92869]

Using recently purchased PMC primers, I reloaded a batch of over 100 rounds for 9mm of various powder charges from light to heavy. After firing them and examining the spent primers I noticed something I've never seen before. In addition to the normal depression from the firing pin there's a very small "pocket" or indentation at the edge of the firing pin depression. I should also mention that all the PMC primers had a small letter "E" stamped on them. The picture below shows a fresh primer on the right side (see the blurry "E"). The left side is a spent primer with the small depression, in this case at about the 9 0'clock position. This occurred on all loads light or heavy. No protrusion found on the face of the slide nor anything on the firing pin tip. Also, on the spent primers the "E" is no longer visible. Anyone experience this?

http://automotivebusinessopportunity.com/9mm-cases.jpg