In days of old there was a cartridge, the 35 Maynard I believe that was a near twin of the 357 Max. When using BP and replica powders in metallic cases, the rule that mustbe followed is no air space between the powder charge and the payload. Experiment at will letting that be your guide, either the bulklet base itself or a wad the bullet rests agaist must slightly compress the powder. I shot a fair amount of Reloder 15 in my 357 Max, would give about 1400-1500 fps with 200 grain bullets, and was surprisingly accurate. My few attempts with black were not as promising and I quickly went back to smokeless, though there is no good reason that BP load should not shoot as well. I was just not determined enough to find it.