Bob: in defense of Hall Sharon, the barrel's manufacturer, this rupture was caused by a second patched ball sitting a few inches above the first charge of pwder and patched ball. The charge was likely in the neighbourhood of 80 gr. FFg and the second patched ball simply slipped back up the bore a few inches. As you can see, the barrel failed right at the chamber area. The plug itself remained in the standing breech tang. Shane was standing at the far right hand end of the line of shooters and it sounded like a stick of dynamite going off. We were having a team stake shoot, so loading fast and hard was the method. We don't do that shoot anymore.
I remember when Blue Jacket, Jerry Cunningham and some others were doing destructive testing with Sharon barrels. I think the results were published in the old Buckskin Report many years ago. I seem to recall they loaded up to 1700 gr. powder, and 17 patched balls in a barrel, with no harm done.
They also took a paper towel tube, wrapped it in duct tape, put a wood plug in one end, and some sort of ball for a projectile. They loaded it with a horrendous amount of powder. No failure of the tube.
The only way they could damage a barrel, was by separating the ball from the charge. I don't recall if they had any totally come apart, but do know they bulged several.
I personally have only seen bulged barrels, generally caused by the use of short starters. I don't use them. Fortunately I have never been around any that completely blew out.