You should crimp all handgun ammunition, and must crimp some of them.
The magnums will produce inconsistent performance unless a heavy crimp is used.
You should use taper crimp for cartridges that headspace on the mouth, and roll crimp for those that headspace on the rim.
I like .002 crimp for 45ACP, 9mm etc.
Lee FCD takes a lot of guesswork out of crimping, the best $10 or so you will spend. I also use Redding roll-crimp dies for the magnums.
P.S. TC - You did not mention the powder for your 38Spec load. 5.1 grains sounds like a heavy load for most powders.