Factory G21 Gen4. .45ACP
Handload well within specifications. No double charge, no bullet setback. The same machine was used to load thousands of rounds before and after without issue.
The barrel and slide were fine, no damage so no double charge.
Bad case head, thin case head walls. Seen this a number of times over the years.

Luckily it was a .45 not a .40, the difference in pressure is why the shooter wasn’t truly injured. (Bruised but no blood)
I did the autopsy on the gun, and sent it back to Glock for a new frame. They agreed with the analysis.

The shooter (cop) called me from the range, I picked it up from where it fell. Never did find the mag catch.