Kyrie,
At the time the French Halifax, above, was produced, a lot of guys would have hand loaded for their guns, especially the rural guys. But, there would have been commercial loads available, and a French guy in those days would have wanted to know a couple of things about his gun. Length of his chambers, level of proof, and what powder the gun was proofed with. Just prior to, and for some time after 1900, proof powders PJ, PS, and PW were in common use, and generated similar, but, not identical pressures to powder T, proof house marking PT. The paper hulls were often used in chambers just a bit shorter than the loaded length of the cartridge.
You would buy cartridges for your gun that matched what the directions said. Usually. It was Americans that maxed out the pressure levels and loaded big load numbers in the hulls and fed them to their guns. And, it was no big deal on the great majority of the repeaters that were in common use.
Shoot ‘em, if you got ‘em.
Best,
Ted
