Can't speak for Lyman or Lee dies, but have used only RCBS. Semi-auto loads (e.g. .40 s&w, .45 acp) head space on the front end of the case, and need to taper-crimp so as not to change the length of the case. Rimmed cartridges (.38 spl, etc.) head space on the rim and can be roll-crimped. At least that's my understanding. Am I wrong?