Gamebore is simply establishing that the shells are in compliance with CIP regulations, which do carry the force of law in the U.K.

The Commission Internationale Permanente pour l'Epreuve des Armes Feu Portatives standards
http://www.cip-bobp.org/homologation/en/tdcc_public?page=1&cartridge_type_id=7
Both 65 and 70 mm 20g standard is SERVICE 830 BAR or 12,038 psi; Maximum SERVICE 950 BAR or 13,779 psi; PROOF 1040 BAR or 15,084 psi.
CIP pressures are measured by piezo transducers (not LUP)

One cannot know the pressure of those shells without a measurement.




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