It happens! But, you had to be going some in order to split the barrel like that - Wow!
So, what was it? Did you fire behind a squib?
Light load. Bullet 1 lodged just past the second blow hole. When the
pressure vented through the blow hole it knocked the slide back just enough
to reset the trigger, and then it just shoved the fired case back into the chamber. Next pull was a "click", I thought a light hit/high primer.
Racked the slide, got back on target, pulled the trigger---you can figure out the rest. Major 9, 124 gr at around 1380fps.
Trashed the barrel, slide, locking block and locking block pin. Everything else is
usable.