My Lee 308 resizing die is collapsing the case necks, suddenly. I was resizing 308 cases before trimming, and all of a sudden the die wouldn't accept the case (as if there is some kind of obstruction, there isn't), and when I finally pushed the case all the way into the die and then extracted the case, the neck was completely pressed in. Any ideas why this would happen? It literally happened in between resizing cases, and nothing changed with the die (that I'm aware of).