For years I would load target .38s' in .357 brass, usually needed to bump up the charge about 10% to match the same velocity. Theory being less bullet jump would be more accuate, well after a time I found the gun was just as accurate in my hands using the 38 cases and I just did a better job cleaning the cylinders after shooting and saving the powder. The problem with downloading .357s' with jacketed bullets too much would be having one without enough power lodge in the barrel. As long as you stayed above the 38+P loadings in the 357 cases you should be alright.