Hi there, my first post here.
Was the pistol a Beretta 96?
I had the exact same thing happen to me with a beretta 92 a few years ago. Situation sounds exactly the same- trigger bar was blown 1/2 way out of the frame, right grip was bent back, powder burns and funny stinging feeling in my right hand, and a blast of hot gasses that hit me in the face, luckily I had eye protection on. As in your case, the brass was pealed back in the unsupported area of the extractor groove.
I was shooting remanufactured FMJ ammunition at the time, it was actually the 2 round out of the box that KB'd on me. There was nothing wrong with the pistol before that as I had fired approximately 100 through it earlier during an IDPA match- I had used factory ammunition then. I'm betting that the cause of the KB was an overcharge of powder, as the recoil and report was very substantial for a 9mm. I no longer trust remanufactured ammo and won't put any of it anywhere near one of my guns anymore.
The good news is that from my experience and probably yours as well, is that the pistol is very well engineered and protected the shooter from any serious harm. Also, I was able to put mine back together, took it to a gunsmith who checked it over and said that everything was ok. I've put at least 5000 rounds through it since without a hiccup.
As for the soft lead- I doubt that that would be the problem. I've shot hundreds of SWCs cast from W/Ws through my beretta- air cooled W/Ws are fairly soft and will scratch with a fingernail. Handguns don't produce enough velocity to cause leading with soft lead so long as its properly lubed- I regularly shoot W/W bullets in my 30-06s and 8mms between 1800-2000 fps with no leading. A bullet that is too hard and/or undersized causes much of the leadign problems. I would still heed the warnign about not shooting lead in Glocks however.