Up until about WWI the standard 20g load in the U.S. was 7/8 oz. with 2 1/4 Dr. Eq. Bulk or Dense Smokeless powder at 1155 fps; in a 2 1/2" case.
7/8 oz. with 2 1/2 Dr. Eq. at 1210 fps had been the standard British 20g load even before the 20g was offered by U.S. makers.

The Winchester Repeater had only 2 Dr. Eq. in 1900

7/8 oz. 2 1/2 Dr. Eq. BULK Smokeless was 8000-9000 psi.
7/8 oz. 2 1/2 Dr. Eq. DENSE Smokeless was about 11,000 psi.


https://sites.google.com/a/damascusknowledge.com/www/home