The Banc D'Epreuves Des Armes a Feu De Liege (Proof House for Firearms of Liege) First Obligatory Proof Load for 12g breech plugged tubes intended for Double-Barreled Breech-Loading Sporting Guns was 21 grams = 324 grains = 11.8 Drams powder and 32 grams = 1.12 oz. shot
For comparison, British Provisional Proof (tube bored, ground, and with chamber cut and threaded for a plug) 1855-1925 for 2 1/2 and 2 5/8 12 gauge shells for a service load of 3 1/4 Dram Eq. with 1 1/4 oz. shot was 9 3/4 dram T.P. (Tower Proof R.F.G. 2) No. 4 or No. 5 Black Powder with 1 1/4 oz. shot.
I don't have a reported pressure for that load, but definitive proof with 6 1/2 Drams and 1 2/3 oz. shot with "Proof House Powder" was about 11,500 psi.
