Bullet fell apart.

[Nyles]

I had that happen with a 1934 dated GECO 9mm Steyr round. Fired the first 7 rounds in the clip beautifully, but on the last one, the case split as it was being fed, forcing the bullet back into it. Had to take the gun apart to get it out, there was powder everywhere. I'm just glad it split on feeding instead of firing!