For all .38 Special loads, standard pressure and +P, I've found a taper crimp to provide better overall accuracy in comparison to a roll crimp. I haven't roll-crimped a .38 Special load in a long time, but, the difference between the two crimps is often slight.

I use a Redding taper crimp die and cast bullets only. These days, I seldom load anything but factory equivalent standard pressure loads. Regardless of the intensity of the loading, I've never found a taper crimp to be inadequate. Granted, there may be some isolated exceptions that I'm unaware of.

Some claim a heavy roll crimp is necessary for heavier loads of slow-burning powder. "Heavy crimp" is a relative "eyeball" term for which no standard exists; some such crimps can distort a bullet to the point of causing inaccuracy.