[Unclenick]

Some cast bullets are formed with a crimp groove, while jacketed bullets often have a cannelure where it is intended that a roll crimp go. In the .357 magnum a roll crimp into the cannelure is used because magnum loads require a hard crimp be present to provide adequate start pressure and to keep bullets in a revolver cylinder from backing out under recoil.

In the .38 special the recoil is less dramatic, and besides, you may well have a taper crimp rather than a roll crimp in your die. The taper won’t get into the cannelure as hard as a roll crimp does. I’d have to look the die set up by part number to tell. In any event, for the simple reason that straight wall case peak pressures go up rather quickly as bullets are seated more deeply, I would use the configuration that seats the bullet furthest out without violating the cartridge overall length requirement. From your description, that would be crimping into the cannelure.