If you're shooting a SWC bullet, rather than stopping at the crimp groove, you can seat the bullet so the top of the first driving band is barely inside the Magnum case mouth and put a bit of crimp over it. That will make the effective case volume similar to a Special case. Obviously, this only applies to loads from the Special table, not any Magnum data.
I've done this with 429421 bullets and seemed to have good results. The caveat would be if the case walls thicken and start to size down the base of the bullet, which couldn't be good for accuracy or leading. I should seat a couple like this and others normally, pull the bullets and measure the bases to see if I can detect a difference.
Recently I started shooting 429667 bullets over 7.8 grains of HP-38, crimped lightly in the crimp groove, which has been giving me excellent accuracy @ 1020 fps, minimal leading, and is a real pussycat in a Redhawk. Even though that bullet doesn't have a distinct shoulder, I was thinking of seating them in until the first sign of a gap between the bullet and the case wall, then adding a tiny bit of crimp just as an experiment with case volume. But I should probably just leave well enough alone, since that load works so well already!