I saw this on the ground at the range this morning. It was the only one that I found. I had read about this somewhere, maybe on this forum. Must have been fired from a Sig, looks like a little firing pin drag to me.
They require special dies to reload. I've got a few thousand of them, but don't think I've loaded them yet. They can *allegedly* handle up to 50K PSI IIRC (assuming your chamber is up for it).