If the owner of the destroyed shotgun ever shows up, I would bet good money he used the wrong powder.
Newish gun
No mods
Well known quality brand
Handload
Hmmm...


People make mistakes. I have seen a number of blown chambers, and everyone was either excess machining forward of the chambers, or inadvertant use of the wrong powder.

If you profile the people that have these malfunctions, it is seldom the new, paranoid, beginner at reloading, that only uses published data.

Just my view of course.

Out there doing it best I can.