About fifteen years ago, when Ken Green was still SAAMI's Technical Director, I called him to ask about the history of SAAMI load pressures in the 357 Magnum. He said they have never changed as far as SAAMI is concerned because the same reference loads were used to calibrate different pressure equipment or as test protocols were modified. So all pressure numerical magnitude changes are equipment artifacts rather than actual pressure changes. The current standards are 45,000 CUP and 35,000 psi, but those numbers come from firing the same reference loads in the copper crusher and the conformal piezo transducer, respectively.
As usual, the CIP's numbers are still different. Their old copper crusher standard had the pressure as 3200 bar (46,400 psi) which is perhaps where the 46,000 psi number came from). Their current transducer limit is 3000 bar (43,511 psi). So their different instruments agree better than ours, but not perfectly, either.
Hodgdon currently lists 125-grain JHP loads (Hornady XTPs) as 21-22 grains of 296/H110. Speer number 8 has 18-20 grains as the range. The old (2004) Winchester single-load, one-and-done charge weight is 18.5 grains. Hodgdon uses Winchester brass but does not indicate the load is compressed. That may not mean much. Before Hodgdon acquired the Western Powder lines and change the website, they listed powder bulk density and VMD lot tolerances, some of which were as high as ±5.6%. So it is perfectly possible for one lot not to be compressed while another is at the same charge weight.
Yes, the 10" barrel used by Hodgdon is an unvented test barrel whose length is measured from the breech face, like a pistol barrel. Their vented (to mimic the barrel/cylinder gap in a revolver) test barrel length is 4", as measured from the front edge of the vent. The 10" barrel is to mimic single-shot handguns.
