As much as I like some Lee products, I would not recommend their factory crimp die on the .38 Special. That carbide sizing ring squeezes the outside diameter of the entire loaded round down to some minimum dimension. For jacketed bullets this is okay as they can probably withstand the sizing but with cast bullets it runs a very real possibility of sizing the bullet in the case down smaller than you want.
With cast bullets (and also with jacketed) the proper relationship of bullet diameter to chamber throat and barrel diameter is essential for best accuracy and to avoid leading. The leading isn�t such a problem at normal .38 velocities but a too-small bullet fired through a normal sized throat will screw up your accuracy.
I�ve played with the Redding profile crimp die in three different handgun calibers. This applies a slight taper crimp as well as a roll crimp, the idea being to increase bullet pull. Good theory but I never saw any real accuracy advantage, and believe me I sent a lot of rounds downrange looking for one. A proper sized expander coupled with a regular roll crimp die works as good as if not better than anything else for revolver rounds.
For the .38 if you already have the Lee 3 die set just use the regular roll crimp die that comes with it.
