CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The High Road, nor the staff of THR assume any liability for any damage or injury resulting from use of this information.
The 357 mag was invented by reaming out a 38 special and then working up loads until the cases stuck and then backing off a safety margin so the cases do not stick.
The SAAMI registered pressure for 357 mag was chosen so that cases would not stick when 357 mag factory ammo was put in any production 357 mag revolver.
To do that, they worked up loads until the cases stuck, backed off a safety margin so they would never stick, and then measured the pressure of the reduced loads.
Hodgdon works up loads with pressure measurement, and tries to duplicate that pressure.
Handloaders buy Hodgdon's data or get it free, and try to duplicate the Hodgdon recipes.
This is layer upon layer of errors.
I cut to the chase, ream out my 38 specials, work up a load with slow powder until the cases stick, and then back off a safety margin so the cases will not stick.
I have no use for Hodgdon data, but I am putting their powder in my modified revolvers.
I make up my own loads.