The G Damascus Parker which Bell blew up with loads of about 30K psi blew in the chamber, specifically between the chamber & extractor rod hole, not down by the forward hand. I do not recall the article stating him adding any obstruction, he simply kept loading to higher pressures till he blew it up. On the afore mention bbl I spoke of with the crack, it was 14" from the breech.
Take it for what you feel it worth & yes I am just a Libery Overall wearing hillbilly, but if you burst a shotgun bbl, any bbl from one built yesterday of modern alloy steel back to one built well over 100 years ago of forge welded horsheshoe stubs & chopped buggy springs & it doesn't burst in the chamber area, look for a cause other than "Too High" pressure.
Jim I would "Bet the Farm" that gun you had was fired with an obstruction if a full investigation had been carried out to determine cause.
I have a German drilling, 16ga, bbl'd with "Prima Kruppscher Fluss Stahl" on which a 3" long section of the entire right side (top rib to side rib) beginning at 10" from breech is "Gone". A WWII veteran had brought it home from Germany & I acquired it from another who he had sold it to. The story I had was the owner at the time had carried it hunting on a day having heavy snow & it burst when he fired it at a rabbit. He assumed he had gotten some snow down the bbl. I assume he was probably right.
Yes a steel bbl can be blown, but compare that with the twist bbl, which I could not even open an existing crack in an area only slightly farther down the bbl.
An obstruction is the most efficient method known to man, to destroy a fine gun bbl, be it steel or damascus.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra