Man I've been missing out, haven't been on THR in a while and this is certainly one of the coolest threads I've ever seen! Had to watch all the videos I couldn't stop. I've had that first photo of the gun on my screensaver for a good while too, since whenever I saw Sharps' post of it, so this is just too cool, the last thing I could have expected to see here on THR after days away from my own computer.
The casing blew my mind a bit too at first. At an indoor range I've witnessed a 1911 accidentally dropped due to the shooter's shirt getting between the gun and holster then the shirt pulled the gun out of the holster. So it fell from tall-person waist-height down onto a concrete floor. It was a S&W (firing pin safety) so it didn't fire, but the base-plate, mag-spring, ammo, and follower went
everywhere.
So I too am currently leaning with the theory that your gun was dropped, discharged due to firing pin inertia, the thumb-safety kept the slide from cycling, and the base-plate, mag-spring, follower and ammo (would compress the spring enough to make the baseplate give under stress) were scattered when the spring expanded.
Just a theory that's not necessarily correct. If that
is what happened however, I wonder if that shot created trouble one way or another, for whoever was carrying it and/or their companion(s), which is why they didn't bother to retrieve their pistol.
I can't wait to see more, a previous post said "I wish TV was this good" and I say amen to that! I hope you can get a time-frame from the casing, and I really hope to eventually see a video of that gun being fired