The 1954 Rules of Proof “Highest Mean Service Pressure” equivalent transducer values as converted from LUP by Burrard’s formula:
2 3/4 tons = 8,120 psi = 560 BAR
3 tons = 8,960 psi = 618 BAR
3 1/4 tons = 9,800 psi = 676 BAR
3 1/2 tons = 10,640 psi = 734 BAR
4 tons = 12,320 psi = 850 BAR
Major Sir Gerald Burrard,
The Modern Shotgun, Volume II, “The Cartridge”, 1955 3rd Revised Edition listed average pressures of a variety of commercial loads (converted 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
(Loads were designed for an “observed velocity” - average velocity over 20 yards - of about 1,050 fps = modern 3’ from muzzle velocity of about 1200 fps)
![[Linked Image from photos.smugmug.com]](https://photos.smugmug.com/Shotshells-and-pressures/Pressure-data/i-P8mkSFd/0/a457e41d/M/Burrard%20The%20Modern%20Shotgun%201955-M.png)
A helpful guide to the question "What load was my vintage gun designed to use?"
