Took my Gen4 19 to the range yesterday to kill a few targets. Had something happen that has never happened with it or any of my Glocks. I've run close to 1500 rounds through this pistol with maybe one or two FTE or stovepipes. Did get some hot brass in my face until I had the new ejector installed but that corrected that issue and it's been running perfectly ever since. Anyway, to the incident yesterday. I was shooting 124gr FMJ American Eagle. Had a fully loaded 15 round mag in it and the first 7 fired perfectly. The 8th round never went into battery, trigger did not reset and it completely locked up the slide. Took the magazine out and could not for the life of me figure out what was wrong. What I did know was that a live round was in the pistol. Took it to a guy who works at the range (not an armorer, but knows what he doing) and he was able to see the round from the top. He put the pistol in a vice and was able to tap the round gently and make it go into battery. All he could figure is the round about to be chambered came out of the magazine at such an angle that it wouldn't seat properly. Truthfully, we really don't know. So we got it to chamber, took it in and fired that round. I ran another box through it perfectly with no malfunctions. A little scary but all seems to be well now. I just wish I knew exactly what made it do it in the first place. Anybody got any thoughts??