Thinking more about Mike's question, IMHO the Birmingham Proof House's frequent proving of pattern welded barrels does constitute an ongoing "experiment'; though without controlling for uniformity of wall thickness.
Great Britain joined the Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives standards in 1980 but the new Rules of Proof were not introduced until 1984. Lead Crushers were used until 1989.
The CIP transducer “Maximal Statistical Individual Pressure” is 850 BAR = 12,328 PSI for a “Maximal Average (Service) Pressure” of 740 BAR = 10,733 PSI, and “Mean Proof Pressure” of 960 BAR = 13,924 PSI.
900 BAR is for a “Maximal Average (Service) Pressure” of 780 BAR = 11,313 PSI and Proof pressure of 1020 BAR = 14,794 PSI.
High Performance (Magnum) MSIP is 1200 BAR = 17,405 PSI for a Service Pressure of 1050 BAR = 15,229 PSI, and Mean Proof Pressure of 1320 BAR = 19,145 PSI.
Damascus barrels reproved in 1992 at 1200 BAR (WHAT were they thinking?!?
)
2006 British Rules of Proof changed the process slightly
https://www.gunproof.com/downloads/rules-proofing
Part IV, “The Proof Load”, Number 27, Part A
Calls for a load of 30% over mean service pressure at a point 17mm or 25mm (about 1”), and at a point 162mm (6.38”) from the breech face a load of 30% over mean service pressure (at that point as determined by the Proof House).
The powder used in proof loads is not specified.
AFAIK the Proof House has declined to reveal the powder used, or if this is one proof load shot or two proof load shots.