Two 2" action flats courtesy of L.D. at Westley Richards Agency, U.S.A.
The first is one of a pair H&H Royal Centenary gun made in 1935; with the standard 1925-1954 proof marks, for 1 oz.
In 1935, the Proof House determined the 2” “cartridge loaded with full 2 1/2” charge...proof of the 2” gun should be identical with the 2 1/2”’.
I don't have the pre-1954 12g 1 oz. standard or max. service pressures
The second is a H&H Royal Twelve-Two, completed in 1934, just before WR changed the name of the 2" guns. The gun was rebarreled in London in 2006 with CIP Standard (Crowed STD) proof.
The
CIP Standard 2" pressures are same as 2 1/2" and 2 3/4"
Maximum Average (Service) Pressure 740 BAR = 10,733 psi;
Maximum Statistical Individual Pressure 850 BAR = 12,328 psi
Mean PROOF Pressure 930 BAR = 13,489 psi