So I took my dad's Springfield XDm .40 subcompact out to the range last weekend. He bought it and then decided his arthritis can't take the short .40 recoil too well so went back to a 9. He only put like 50 rounds through it. I grabbed a box of my factory loads and a plastic box of his .40s (which I thought were factory Winchesters) and took my spot in the lane. Popped off 3 mags worth with my ammo and didn't think there was much difference in recoil compared to my .40 Sig. Loaded the next mag with the rest of my ammo and then a few of his. pow-pow-pow through the end of the factory loads and then BLAMMO! Concussion about knocked me on my rear end. Pieces of brass/unburned powder peppered my forehead. I put the gun down on the bench and stepped back to gather myself. I looked at the gun and saw the slide was locked back and at first semi-concussed glance I thought I had a stovepipe that somehow detonated the round... But upon close examination it's obvious the back of the cartridge ruptured and blew out the chamber. Thank god I was wearing eye pro!!! My hand took a beating but no breaks or blood. (I was shooting lefty.) I'm also very thankful this happened in an enclosed pit otherwise my wife may have caught some of it in the lane next to me. I've seen cartridges rupture before but never out the rear like that. I checked the box of ammo and saw that dad has some rounds (I'm guessing reloads) of unknown origin in there mixed in with Winchester brass. There's no way to be sure but I'm guessing I hit a hot round. I wonder if the match grade barrel saved my hand from a complete rupture? Going to send the whole thing in to Springfield to see what/if any of it can be saved.