PS No user error. I was just pumping the action to load a round into the chamber. On the forward motion, before it reached the chamber, it turned downward and the face of the shell dropped straight down while I tried to close the action on the shell rim, which was blocking closure. I then looked at the gun and saw what you see in the picture I provided.
I've had pump shotguns since I was seventeen. In fact, I had a Mossberg 500 back then. Never had a problem with it.
PPS The Mossberg 500 in question is still in the family. I sold it to my brother in law at some point, and then he sold it to his son, my nephew, who's a cop. Still works great.
