Wow! Barrel looks fine so obstruction not likely. So what can cause such destruction to action failure and not visibly show damage to barrel? This was massive over pressure to action obviously. Not many things can do that except for wrong powder, overcharge, metal fatigue, lug failure? Case head separation should not cause this if action vents.
I hope we can get good investigation with valid cause and effect analysis so we can all learn from it.
Every time we see a serious incident like this, is a sobering reminder to double check our own reloading procedures, checks and audits of them to validate our own safety steps.
Fortunately the shooter was not harmed!