9mm headspaces on the forward rim of the case. If that was distorted in some way, whether it hit the ramp on the way in, or the front of the mag or slide stop, or if it just came out of the loading machine that way, it would not have taken much to prevent it from fully seating. A little less, the gun goes into battery and this thread does not exist. A little more and the gun refuses to fire. OR, since the gun has not been fired since, maybe a mechanical problem with the gun prevented it from going fully into battery. I think the slide lock lever pin has to be round, the channel under the barrel has to be clear and not buggered up, the breech face has to be smooth and not have something stuck on it or the extractor. Not having the gun in hand we can not determine that, but I am convinced the damage to the case is totally consistent with premature extraction. And you can NOT cure that with a little blue pill.