I’ve read, the sum total of my knowledge, that the problem can arise from the projectile not being firmly seated is due to the air being compressed by the explosive effect of the black powders detonation.While this example strengthens the warning to make sure the ball is not short started, there is more information that is lacking to tell the full story. It is stated that the barrel was a smoothbore. It appears from the set triggers that this firearm started out as a rifle and the barrel was later bored out to be smooth. I would be interested to know what the size of the barrel was across the flats, what was the barrel bored out to and was this a ball or a shot load that burst the barrel. Because of the perceived modification to the barrel, I don't think that identifying the maker of the rifle is as pertinent as the other information.
Question I have would that compression reach a greater PSI than the black powder its self reached.
The complete destruction of the firearm pictured would be from a very high pressure level it seems. Air or extreme powder charge. ??