Just a reminder
Great Britain adopted the 1969
Commission Internationale Permanente pour l'Epreuve des Armes Feu Portatives standards March 1, 1980 but continued using Lead Crushers to measure pressure 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 930 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.
In 2006 the British Rules of Proof were modified
http://www.gunproof.com/Proof_Memoranda/RULESOFP.PDFPart IV, The Proof Load, Number 27, Part A
The standards call 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).
It is possible that the pressure at the location of the seam is higher than with the former proof load?
To my knowledge the Proof House uses a
single proof load to generate those pressures, and has not revealed the powder (or combination of powders) used in the proof load.
