DISCLAIMER: don't follow arbitrary advice on a forum. Ok with that out of the way, FWIW I don't crimp my 30/30 loads anymore; with
my specific load. They don't get set-back. But I'm loading for accuracy.That's 21gr AR2207 under a 150gr pill @ 2000fps. I have tonnes of different FLS dies for the 30/30, and I just settled on the one that yields the most tension, which coincidentally is a hornady die.
I agree with SCJ - I'd be aiming to take the crimp out, if possible, mainly for brass life. But
only if you're shooting reduced loads - full-power 45/70 loads are gonna boot. You could experiment with shooting, then measuring the OAL of the incoming rounds in the mag. I do that with all my levers to decide whether or not to crimp - but I only neglect the crimp for reduced recoil, target loads.
Just my 2c. Others will angrily disagree, at which point I will refer you to my disclaimer at the top.