Long version
British 1896 Rules of Proof Nitro Powder Pressures
Sporting Guns and Gunpowders: Comprising a Selection from Reports of Experiments, and Other Articles Published in the "Field" Newspaper, Relative to Firearms and Explosives, Volumes 1-2, 1897
https://books.google.com/books?id=inQCAAAAYAAJ “New Rules of Proof”
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA7&dq“Under the 1896 Supplementary Nitro Proof Rules, the Nitro Proof Charge was not fixed. It could be changed by the Proof Houses as existing powders changed or new products released. The Proof Houses would determine the charge in order to keep the pressure 80 - 100% above that of the Service Charge.”
Short version SERVICE pressures
Nitro 1 1/8 oz. with 42 grain Bulk Smokeless = 3 Dr. Eq. (1200 fps): 5330 - 6110 psi
Nitro 1 1/4 oz. with 45 grain = 3 1/4 Dr. Eq. (1220 fps): 6360 - 8620 psi
PLUS 10% by piezoelectric transducer measurement
