Since you've got no replies so far, I'll take a crack at it. It appears pretty clear from the evidence you've given that the hot stuff is recoiling to the extent that a live round is jumping off of your magazine behind the chambered round and almost always making it out of the slide before it closes. If you hadn't have caught that live round stovepiped, I woulda had a hard time believing it could happen. It just seems weird that there is enough time for two rounds to get out in one slide cycle. You might want to check your magazine's feed lips. If they are worn or broken you could get a jumper during stout recoil. Good call on retiring that ammo for any serious use. I suppose you could shoot it recreationally until its gone, but I'm glad you never had to rely on it for SD.
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