Miller's assertion is right on I would say. They were proofing for a certain pressure
so what they used is not that important.
The first proofs were done according to the St. Etienne proof house's rules dating to
1866:
-For 12 bore: 10 grams of black powder and 70 grams of nº8 shot.
Later (1920) there were different levels of proof ranging from:
-First proof: 11grams of BPnº2 and 70grams of nº8 shot for 941 kg/cm2 pressure
-Finished barrels: 10grams BPnº2 and 60grams of nº8 shot for 791 kg/cm2 pressure
-Superior proof: 14,5grams BPnº2 and 75grams of nº8 shot for 1133 kg/cm2
-Double proof: 20grams BPnº2 and 120grams of nº8 shot for 1441 kg/cm2
-Triple proof: 30grams BPnº2 and 180 grams of nº8 shot for 1726 kg/cm2
The BPnº2 is called in French "Poudre Noire Forte Nº2.
The above for 12 bore.
JC
