It is reassuring that Sherman Bell's destructive test of the Parker Vulcan Steel VH and 3 Iron Damascus GH took about 30,000 psi to burst.
The GH testing started at 11,900 psi and one chamber ruptured at 29,620 psi. The VH started with a Proof Load of 18,560 psi. Both chambers bulged at 29,620 psi and ruptured at 31,620 psi.

Proof and standard service load pressures have not changed much in 130 years despite all the new fangled low alloy barrels.
Dense Smokeless did run about 1000 - 1500 psi higher than Bulk Smokeless

Forest & Stream, November 24, 1894
“Gas Pressure or Bursting Strain”
https://books.google.com/books?id=19kwAQAAMAAJ&pg=PA459&lpg
The proof-house charge of the American Testing Institution for a 12-bore gun develops a gas pressure of over 18,000 lbs. to the square inch. (By LUP so transducer number would be 10-14% higher)

English 12g service & proof pressures + 10-14%
Field, November 26, 1892
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA296

"E.C.", "Schultze". and "S.S" all bulk powders

[Linked Image from photos.smugmug.com]

[Linked Image from photos.smugmug.com]

Smokeless Powder Co.'s “S.S.” (Smokeless Shot-gun) was a 43 grain = 3 Dr.Eq. Bulk powder that didn't last very long because of pressures turned out to be higher in 16g and 20g

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