The G.E. Lewis "Magnum" 3" with 1 1/2 oz. shot 12b were introduced c. 1920 (before Olin's Progressive Burning Oval)

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Major Sir Gerald Burrard, The Modern Shotgun, Volume II, “The Cartridge”, 1955 3rd Revised Edition reported pressures (converted from Long Tons/ Sq. Inch)
10g 2 7/8” 1 7/16 oz. 4 Dr. Eq. standard service 9,296 psi with maximum service 11,984 psi
12g 3” 1 1/2 oz. 3.57 Dr. Eq. standard service 9,632 psi with maximum service 12,320 psi