Minus, to clear up confusion:
The magnum or standard primer issue is based on the powder used, not the caliber. If you have any questions on which is correct for your chosen powder, contact the manufacturer of the powder in question, and they'll clear it up for you.
As for the load you put together, I don't know if it's safe or not, I've never used that fast of a powder in 357 magnum applications. I do know that regardless of caliber, folks that load 231 seem to use standard primers almost exclusively.
If you used winchester primers, and that load is listed in current manuals you should be fine. Winchester makes "one-size-fits all" primers, for both standard and magnum applications. If that load is at the top of the charts, and you've used a dedicated magnum primer from say, federal, CCI, or remington, I would be a little leary of it, unless you're launching it out of one of the larger framed/stonger 357(N-frame, GP100, redhawk, etc.)