Looks to me like the brass let go and the gases were diverted into the magazine/trigger area.
If it was over pressure the extractor probably wouldn't still be in the gun.
All the so called Kabooms floating around the internet have the chamber area of the barrel peeled back and that shows a waaay over pressure load and not a fault of the design.
Stray Round - very good observation.
I have to admit, I really didn't pay much attention to the photos, I was more interested in the "spin" certain individuals, from Glock lovers to Glock haters, would put on this issue. But your post forces me to look at the photos and I'm left with a similar conclusion.
The gun in the photos does not exhibit signs of an over-pressure situation. Now the barrel peeling you talk about is usually indicative of a barrel obstruction. But still, in most over-pressure situations the damage to the gun is much more severe. You're right in that the extractor is often blown out. But with an over pressure situation, the dammage to the frame is usually quite graphic and catastrophic. Whereas this pistol doesn't have nearly the damage you normally associate with an over-pressure round.
This pistol looks like your typical G23 that's been fed reloaded ammunition. Now whether it's a case of the owner shooting his own or someone elses reloads, but then stating to everyone that it was factory, I don't know. Or perhaps it's a factory reload; there are many makers of very high quality reloaded ammunition, Black Hills is one such maker.
Now understand, this is anecdoatal, looking at a picture and my opinion is just that, and opinion. But to me, that looks like it was fed a reloaded cartridge.
