In a 1927 Western Cartridge Co. flyer "Super-X The Long Range Load" by Capt. Chas. Askins, the 12g. duck load is described as 1 1/4 oz. with 38 1/2 grains or 3 1/2 dram DuPont Oval with a muzzle velocity of 1400 fps and a breech pressure of 3 3/4 tons or 11,480 psi; just below the current SAAMI 12g maximum of 11,500 psi.
From “Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics” by Wallace H Coxe; E.I. du Pont de Nemours & Co., 1927, a DuPont Oval Pamphlet, p.20.
The original 1922 Western Cartridge Co. 12g ‘Super-X Field’ (loaded with DuPont Oval), and 1923 Peters Cartridge Co. ‘High Velocity’, United States Cartridge ‘Ajax Heavies Long-Range’, and Remington Kleanbore ‘Nitro Express Extra Long Range’ loads were all 2 3/4”, 1 1/4 oz., 3 3/4 Dr. Eq. (1330 fps).
Dram Eq. is listed as 3 but
has to be 3 3/4 compared to other pressure graphs.
Charge was 1 1/4 oz. Pressure is expressed in Long Tons.
Using the estimated Tons Lead Crusher Pressure (Cp) conversion to PSI (pound force per square inch) (Cp x 1.5) - .5 = TSI, TSI X 2240 = PSI.
"Ballistite" Dense maximum pressure at 1” was 4.9 Long Tons = 15,344 psi
"Schultze" at 1 3/4” was 4.5 Long Tons = 14,000 psi
DuPont Bulk at 1 2/3” was 4.1 Long Tons = 12,656 psi
FFFg at 1 1/2” was 3.8 Long Tons = 11,648 psi
Oval at 2” was 3.5 Long Tons = 10,640 psi
A DuPont loading manual from the 1960s listed DuPont Bulk:
3 1/2 Dr. Eq. with 1 1/8 oz. shot at 10,000 psi
+ 10-14% by modern piezo transducers3 1/5 (3.20) Dr. Eq. with 1 1/4 oz. shot at 9,900 psi
In the 1928 edition of "Smokeless Shotgun Powders", Coxe reported
3 1/2 Dram Eq. 1 1/4 oz. loads:
DuPont Bulk smokeless powder - 11,700 psi by LUP
Schultze Bulk smokeless powder - 11,800 psi
28 grains of Ballistite - 12,600 psi
40 grains of DuPont Oval Progressive Burning powder - 9,400 psi
I have no data for Western's 3 inch 'Record' with 1 3/8 oz. of shot released in 1924; U.S. Cartridge Co. 'Climax Heavies' was introduced in 1927.