Great Britain joined the Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives and adopted the CIP standards in 1980 but the new Rules of Proof were not introduced until 1984. Lead Crushers were used until 1989 when BAR was introduced, and the imperial proof marks could be requested from 1984 to 1989 using the Tons SERVICE pressure while the metric version used the Kg PROOF pressure.
The CIP transducer “Maximal Statistical Individual Pressure” for 50mm, 60mm, 65mm and 70mm 12g 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. Max. fps is 1,300 fps.
High Performance (Magnum) MSIP is 1200 BAR = 17,405 PSI for a Max. Service Pressure of 1050 BAR = 15,229 PSI, and Mean Proof Pressure of 1320 BAR = 19,145 PSI.
Both 65 and 70 mm 16g standard is SERVICE 780 BAR or 11,313 psi; MSIP 900 BAR or 13,053 psi; PROOF 980 BAR or 14,214 psi.
(The original 1984 chart indicates 16g PROOF 1020 BAR = 14,794 psi. The number was revised to 980 BAR in 2006.)
Both 65 and 70 mm 20g standard is SERVICE 830 BAR or 12,038 psi; MSIP 950 BAR or 13,779 psi; PROOF 1040 BAR or 15,084 psi.
(The original 1984 chart indicates 20g PROOF 1080 BAR = 15,664 psi. The number was revised to 1040 BAR 11-2021.)
Shot weight is not considered in the CIP standards
I don't know if British shell boxes are still labeled:
These cartridges are suitable for use in:
70mm case length: Guns with a chamber length of 2 3/4” or longer, nitro proofed to a service pressure of 3 1/4 tons per square inch (900 kg per square cm)
67 mm case length: Guns with a chamber length of 2 1/2” or longer, nitro proofed to a service pressure of 3 tons per square inch (850 kg per square cm)
