Probably the best data as to loads and pressures of British shells under the 1925 and 1954 Rules comes from Major Sir Gerald Burrard, The Modern Shotgun, 1955, 3rd Revised Edition Pressures converted to transducer psi from Long Tons/ Sq. Inch at 1”
12g 2 1/2” 33 gr. Nobel Smokeless (3 Dr. Eq.) with 1 1/16 oz. - 7,885 psi
12g 2 1/2” 33 gr. C&H Smokeless Diamond (3 Dr. Eq.) with 1 1/16 oz. - 8,288 psi
12g 2 1/2” 31 gr. Smokeless Diamond (2.8 Dr. Eq.) with 1 1/16 oz. - 7,179 psi

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