Keith, I am not familiar with any definitive testing of the results of a primer in the powder charge accellerating the ignition to a dangerous pressure. However, I have read of barrel failures that seemed to have eliminated other obvious causes. Some testing of the effects of a primer added to the powder charge would be interesting. Some loaders (the machine, not the person) effectively eliminate the possibility. Some loaders make it more possible by design. Some loaders (the person, not the machine) leave powder cannisters open, making it possible for a loose primer to drop into the powder cannister. Bad idea. On another aspect of this discussion, I think it is very unlikely that a wad would be left from a previous discharge close enough to the breech to cause the pictured blowup. I also think it is rather ridiculous to be discussing a barrel blowup without first eliminating the possibility of thin walls.
