In those few instances where I will use a compressed load of slow powder in a large capacity case, I will use a SLIGHT crimp, with a Lee special die for this, to do two things. One is to keep the bullet from "creep" due to the pressure on it's base from the compressed charge and the other is to keep the case neck tension as "equal" as possible among the rounds.
This, is a trick we older shooters learned back when H-4831 "surplus" was THE slow powder and we used it for dammed near every larger case from .25-06 to .340 Weatherby. Now, that we have so many denser powders, RE-25, etc., this is less useful than it formerly was; however, I still like to use a slight crimp on loads for my .375H&H rifles as the bullets can "creep" under recoil.
I ALWAYS crimp my 450 SAF loads in my .458WM and would with any cartridge over the .338WM, just for the most consistency possible. I have a Corbin tool for putting a cannelure on any bullet where I want it and, used carefully, this can improve hunting ammo handloads....but, it is a major pita to do when loading for many large bore rifles.
Experiment a bit at your range and see what happens, WORK UP CAREFULLY as this can spike a load and be especially cautious with trimming to EXACT length for EACH case. HTH.
