Miller,
As to whether other proof houses do/did as you say, I have no clue. But, per Lee Kennett's excellent article on French proof in "The Gun Digest" 24th edition, 1970, A smokeless proof powder load was developed for each early smokeless powder as it was introduced. Superior proof of finished arms HAD been done with black powder, prior to 1896. The proof load for powder J, and it's derivatives, J1 and J2, and powder S were introduced in 1896. Powders M, R, and S2 had their smokeless proof loads developed in 1898, and powder T in 1900.
By 1914, all but powder T had been dropped as proof powders. Powder T is still manufactured to this day.
If what you are claiming is true, there would have been no need to develop a proof load for each powder as it was introduced-which was not the case, according to Kennett. Also, according to Kennett, these proof loads varied considerably in their pressures. It would seem to have been important, at least where French proof was concerned, that a gun intended to be used with powder J, M, S, or T, or any of the derivatives, be proofed with said powder. Which, as I pointed out, is what I thought they did.
Look it up yourself.
The rules of 1928 changed much, but, black powder proof of shotguns was set at 8,800 and 11,400 for superior black powder proof. Proof with powder T was set at 12,000 PSI and 15,600 for superior smokeless proof. Note that smokeless proof is performed with powder T. Not black powder.
Believe what you want about other proof houses, I guess. They aren't relevant to this conversation.
Best,
Ted
