My kingdom for a Korth (or Manurhin)?

[zeleny]

Correct, CUP and PSI are two completely different measurements.

From what I’ve gleaned, there’s not even a formula for converting one to the other.

Opinions differ: Denton Bramwell, “Correlating PSI and CUP”, 2002.

[jtcarm]

That... I don't think that's right.

I don't know how they were measuring velocity in 1957, but the purpose of canister grade powder is to be consistent from lot to lot. Unless 2400 got nerfed years ago and I don't remember it, I can't imagine getting 1500fps out of a real world 6" gun with a dose at 15.5gr.

I've shot plenty of the old 14.5 standby and I think I got about what you'd expect a standard .357 to get out of a 4" barrel. I want to say mid 1200s but I could be misremembering. I know for a certainty that specific 686-5 has been crono'd on two different occasions with two different lots of Remington 125gr SJHPs and got over the cataloged 1450fps both times. So it's not like the barrel is slow. I doubt 1 grain is going to yield 300fps.

Lyman had to be using a long test barrel to get that.

My Lyman manuals don’t go back that far, but IIRC they used a universal receiver, so no B/C gap and it probably had a good bit of free-bore.