I believe most documented with images blow-ups shown on this or other shotgun related internet sites in the last 10 years are documented here
http://www.picturetrail.com/sfx/album/view/17546456
http://www.picturetrail.com/sfx/album/view/24513874
http://www.picturetrail.com/sfx/album/view/24519472

and the vast majority are rationally explained by:
1. obstruction
2. thin barrels
3. over-pressure loads
4. "inexpert" chamber and forcing cone lengthening



Damascus barrel welds do fail



and may have inclusions



And this, I believe, was caused by smokeless powder detonation, but we REALLY do not want to go there
http://www.trapshooters.com/threads/shotgun-blowups.244114/
http://www.trapshooters.com/threads/smokeless-powder-ddt.245629/


https://sites.google.com/a/damascusknowledge.com/www/home