More numbers very similar to today's 16g loads for you Mark
William Bruette,
Guncraft: Guns, Ammunition, Wing & Trap Shooting, 1912
https://books.google.com/books?id=5g51K93as84C&pg=PA210&dqPressures converted from long tons/sq. inch to psi by Burrard’s formula - no need to add 10-14%
Curtis & Harvey’s (42 gr. = 3 Dram) Amberite (Bulk)
16g 2 1/2” case 36 gr. (2 1/2 Dram) 15/16 oz. = 10,640 psi
Curtis & Harvey’s Smokeless Diamond (33 gr. = 3 Dram)
16g 2 1/2” case 28 gr. (2 1/2 Dram) 15/16 oz. = 11,480 psi (SAAMI max. is 11,500 psi)