Couple of things that apply to the 357 magnum.
When the 357 Mag was designed and guns built for it, the pressures accepted by SAAMI were 47,500CUPs. That's in the ballpark with some rifle cartridges. As the guns of the day, primarily S&W, wouldn't stand up to the beating, SAAMI lowered the pressures to 45,000CUPs. Still a hefty round. Today, SAAMI accepted pressure is 35,000PSI. While there is no direct comparison between CUPs and PSI, there's been a tremendous reduction in the power of the 357 Mag. Frankly, they should drop the Magnum from it. The reason for the pressure reduction per SAAMI is that they were seeing a lot of import guns that folks were buying that would just not hold up to the pressure of the 357 Mag. So they have basically neutered it to keep the cheapy crap pistols from hurting someone.
Yes, the J P Sauer pistols, primarily the Western Marshal, are actually made on retired Colt machinery. This was a deal back in the 70's as I remember correctly and many of the parts will interchange with a Colt. The action and gun are as strong as a Colt and the 44 Mag has taken many a load that exceeds SAAMI limits and keeps on ticking. They are a pretty slick revolver. I've had several over the years that I've taken in trade and only had one that I didn't like- I couldn't keep the ejector rod on the barrel on a nickel 44 mag. The 44 also has grips that are far too small for my large hands but the 357s have been tack drivers. I wouldn't worry about max loads in a Hawes/Sauer pistols. They will take the original pressures all day long. I ran thousands thru the ones I had with zero issues.
Yes the load pressures will be reduced. By how much would be a guess. I wouldn't suggest a guess when it comes to reloading. Either use data that is published or forget it. While you may go up a tenth or so, the "or so" could put it in the danger zone. Not all powders burn with a linear line of pressure build. Some will work great for mild to medium pressure loads but then pressures will spike. The data takes all of this into account so unless you KNOW what yer doing- don't.
