My guess is that the "infamous" unsupported chamber associated with Glock barrels and their clones is the culprit. Note that the case did not have a lengthwise split. I have fired much Federal 9BPLE. In a Colt 1911 one of these +p+ rounds cracked a locking lug and bent the ejector. I suspected that loose case mouth tension permitted the bullet itself to set back into the case. This may have occurred in Lon's event. My bullet case was not damaged but did have a flattened primer. Another factor in my instance was that some of this ammo had been chambered and ejected two or three times, and yes I got the problem round out of a gallon can on my bench. I like this Federal round, but now inspect each and every single one before loading it.