August, 1922 Outdoor Life
https://archive.org/details/sim_outdoor-life_1922-08_50_2/page/120/mode/2up
28 gauge Plus 10 - 14%
5/8 oz. 2 Dr. Eq. = 8,714 psi
3/4 oz. 2 Dr. Eq. = 10,259 psi
3/4 oz. 2 1/8 Dr. Eq. = 10,998 psi
7/8 oz. 2 Dr. Eq. = 12,387 psi

DuPont Brandywine Experimental Station data cited by Charles Askins in 1933
DuPont Bulk Smokeless Powder.
28g 2 Dr. Eq. 5/8 oz. = 10,438 psi