Indeed lagopus

Major Sir Gerald Burrard, The Modern Shotgun, 1955, 3rd Revised Edition Pressures converted from Long Tons/ Sq. Inch at 1”

Standard Load.....................Standard Service........Max. Service
12g 3” 1 1/2 oz. 3.57 Dr. Eq.........9,632 psi.............12,320 psi
(1 1/2 oz. with 3 3/4 Dr. Eq. is 1260 fps)
12g 2 3/4” 1 1/4 oz. 3 1/4 Dr. Eq...9,296 psi.............11,984 psi