Brass will work harden that is why you see annealing on military brass. I have reloaded some PPU brass several times and I still have it in rotation 9mm, 223 I don't think I have any 10mm PPU.( I think I would have come up with a different name for my company besides Double PU). I really didn't read all the post I just watched the video and looked at the pictures and read what the shooter said since he was there. I have had a few case raptures nothing dramatic and that was from over used brass. I have never had a head separation. Since there was no barrel or slide damage I could see from the pics this was the only thing I think could have happened. Projectile excited the bore hit the target. We are talking micro seconds. Delayed blow back works because the case is stuck to the chamber wall because of pressure. When the pressure goes down from the projectile exiting the barrel the slide unlocks and extraction begins under normal shooting. It takes several 1000 psi to stretch the brass to seal the chamber. So I am saying the psi need to stretch the brass did not happen fast enough allowing the slide to unlock and the extraction to start. As the psi went up the brass that had been extracted could not with stand the pressure and failed. As we get have mistakes we learn from them hopefully never to repeat them. When things like this happen we are luckily to have them on video and the shooter documents everything as well as they can so we as shooters learn from these things. I am very glad nothing but a few scrapes and bruises happened to the shooter. Underwood is replacing the damages to his firearm along with his underwear. I hate this happened but there is a lot to gain from this and to be happy for.

Ok undersized bullet causes a set back which changes the burn rate of the powder. Since I'm not a balliectis expert I'm just adding my 2 cents here. Compressed powder load in a rifle makes the power burn slower and with the projectile undersized and excited the barrel and there was no barrel or slide damage I would say the brass did not reach proper PSI to seal the chamber and lock the barrel into place. I agree recoil springs aids in the locking time but doesn't hold the slide into battery the pressure of the cartridge does.( Cool how John M. Browning was able to figure that out over 100 years ago).So the barrel unlocked prematurely causing the extraction to start and then the full PSI was more than the brass could handle causing the brass to rupture sending the gasses down the mag well causing the frame to hold just enough to keep the shooter from losing a hand. Seems like the pistol worked liked it was designed to. I don't like Glocks but that does not take away from them being great firearms. To me it's Ford or Chevy thing. Not saying anyone is wrong but the physics and mechanics is what brought me to my conclusion.    I could be wrong but it is really early in the year for that. I tell my wife I'm human I get once a year to be wrong.

Just want to say I have been on this site a lot just looking around especially at the factor pull downs. I have been reloading for almost 40 years and found this site has the best reloading data for the 10mm that I can find. I have scoured all the old reloading manuals and the internet  but none of them holds the wealth of load data here.
I am married lets see for 32 years to my first and only wife and I have a 13 year old son who loves shooting as much as I do. The 10mm bug hasn't bite him yet but I do believe it will not be long before it does. He loves the 9mm and now that my eyes are getting old he is out shooting me. But not as fast as I am in IDPA. I love the 1911, and S&W M&P. My EDC is 90% 1911 a RIA TAC 2 in 10mm that I have semi customized. I am at ruffly 3000 rds through it and the only problem I have had was the front sight became lose. A little peening and some red loctite now it seems to be rock solid. Just wanted to say hello to everyone.