I have one comment about loading .38 SPL cases loaded to .357 Magnum ballistics: Learn to write with your weak hand!

As a matter of personal policy, I don't overload .38 SPL. I don't underload* .357 magnum (below minimum specs). I don't give away hand loaded ammunition.

Powder that is too loose or too compressed can have unpredictable pressure spikes. Case capacity between .38 and .357 is nominal, but you can't be too safe.

I shoot pistol caliber carbines, including .357 Magnum. A light load might not push the bullet out of the barrel. If that happens it sounds like this -- "click". That's right, nada, no sound other than the hammer falling. You'll hear the next one okay.