Wouldn't be too concerned about a 9mm cast in a .38/.357 revolver - especially since they seem to do the trick.
Just for grins, throw a caliper/micrometer on your as-cast bullets to see what you're getting. Depending on the allow/mould size, you may well be over an "acceptable" size anyway. I've a .309" diameter mould that throws right at .315" & the .309" sizer sizes to about a 1/2 thou of that - go figure. But they still shoot very well indeed.
Easy on the crimp as mentioned & since it ain't broke, what's to fix?