Larry,
Proof with powder J, no matter the type of gun, or which version of powder J, tells you all you really need to know.

It isn't proofed with a modern, smokeless powder. You should adjust your loads and use accordingly.

I never suggested we ignore that. But, no matter which version was used in what gun, it was still marked, at the time of proof, as proofed with powder J.

And that is all you, or I, as non leading ballisticians, who aren't writing books on that subject, really need to know.

Best,
Ted