hard to believe that magnum pistol should be crimped because of slow burning powder, but Rifle powders( that are even slower) folks suggest a slight taper crimp ?
If you are doing your own loading, try different crimps. See what works best for you.
Right now, Im working on the same project. My best loads are being subjected to the standard Lee taper crimp dies,then I have some run thru their factory roll crimp die.
Soon as the weather breaks, Im hitting the range, maybe you should do the same? This is the fun part of reloading,, trying different things.