[SL1]

I don't have all 3 of the Accurate Manuals that Clark references, but the one I do have showes that they shot the data with the CUP measurement method, which has a SAAMI pressure limit of 45,000 CUP. The pressure that Accurate showes for 15.0 grains of #9 powder is 44,900 CUP. There really isn't any agreed-to conversion from CUP to PSI, but a reasonable guess is that 45,000 CUP in a .357 Magnum cartridge is a little over 45,000 psi.

On the other hand, the Hornady data was probably produced with the PSI measurement system. SAAMI adopted a maximum pressure of only 35,000 PSI for that system, and loads and velocities with the newer system are obvious reductions from what was obtained with the old CUP system. For what it is worth, my older Hornady #4 manual lists 14.3 grains at the top end of its chart, and that was probably shot with the CUP system. And, Hornady's charge vs velocity tabular format only tells us that 14.3 grains produces 1450 psi and that the next increment that would produce 1500 fps is not recommended. Extrapolating the #4 data would indicate that something like 14.7 or 14.8 grains would have produced their 1500 fps table entry, so that is still a little lower than the Accurate max at 15.0 grains. But, it is a lot closer.

That is why I think you have data from two different sourcse that are using different measurement systems and different pressure limits, rather than just seeing the usual effects of different lots of powder, etc.

Note that the SAAMI pressure limits for the 44 Magnum were similarly reduced in the PSI system.

SL1