so SAAMI plays it safe and keeps the pressure artificially low.
Much as I hate to defend SAAMI about their pressure limits, you've got it exactly backwards.
SAAMI isn't keeping the pressure artificially low in this case, you are wanting to jack it up artificially HIGH.
You want to load the .38 short case to .357 magnum pressures, for use in a .357 Magnum gun, ok, its your gun, your ammo, and your business. Though I do wonder why on Earth you would do it. Is it because the short case loads and unloads a fraction of a second faster (in a DA revolver)???
I don't see what possible use that would be, and since we aren't at the end times just yet, and real .357 & .38 Special brass is available, I don't know why you're doing it.
If you're a responsible person you should take precautions to ensure your short colt magnums NEVER end up in anyone else's hands. (including after you pass away...) So, I don't think its a very good idea.
That being said, lets look at the technical aspects, and for now, ASSUME working up to .357 pressure is allowable.
You've got dies (Lee) so you can crimp the short case. Which is important, because if you get close to .357 level, you're going to get .357 recoil.
Next question is how much volume do you have to work with?
the 38 Short Colt actually has slightly greater case capacity than the 9mm.
Ok, if this is correct, then fast pistol powders will do better, medium ones will work and the slow "magnum" powders are a poor choice.
There's a reason people don't load 2400, H110 or W296 in 9mm Luger size cases. And, for what its worth, the K frame .357 is not a super strong gun.
So, watch your brass carefully. I don't know when you will start seeing flattened primes (if you ever do) but I'll tell you the one pressure sign you must not ignore. When fired cases stick in the chamber, and cannot be ejected NORMALLY by hand, brother you are DONE. Back off that load at least a couple tenths grain. or more!
IF you want to give your loads here, be sure to include the "sticky" warning (copy and paste it into your post) about loads exceeding published data.
Doing what you say you want to do puts you completely "off the map" and entirely on your own.