Bro. Venters came through, and his article "The Short-Shell 12" in May-June 2017 Shooting Sportsman is a must read

2" proof and service pressures were the same as 2 1/2" - 3 Dr. Eq. with 1 1/8 oz. shot with a mean pressure of 3 1/4 tons by LUP = 9,800 psi by Burrard’s conversion.

[Linked Image from photos.smugmug.com]

2 inch "metal cartridge loaded with full 2 1/2" charge may shortly be a standard British cartridge (and) proof of the 2" gun should be identical with the 2 1/2" "

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