The Lee FCD is a different type of crimp die for autos (actually a more sophisticated taper crimp die than a standard taper crimp die, as well as having the function of resizing the complete cartridge) and revolver cartridges (a roll crimp and cartridge resizing die). In either case, Lee says it is not possible to over-crimp and distort the cases. The Lee Taper Crimp die, on the other hand, is a standard taper crimp die. Lee says it is primarily offered to replace those Lee made prior to 1986 (or is it 1985), primarily applicable to auto cartridges. In fact, I understand that it is now the "standard" seating/crimp die included in current Lee die sets for cartridges that headspace on the rim (most semi-auto cartridges), though I certainly could be wrong.

I recently started using the FCD in reloading .45 ACP, and I can only say it is a real improvement. I set up the standard seating/crimp die for seating only, with no crimp, and place the FCD in the next station. Once properly adjusted, it results in extremely consistent rounds, even with mixed brass, excellent headspacing, excellent chamber fit and consistent feeding in all my 1911s. I'm convinced - I will get another for 9mm (when I get around to reloading it, just don't shoot a lot of them), and plan to try them for .38/.357 and .44 Mags, as well. I do have them for .308 and .30-06, haven't tried them in the rifle calibers yet, though. I expect good results in that application, as well (a different system altogether from the handgun caliber FCDs, BTW). My bottom line recommendation - try the FCD, I bet you'll like it. If you don't, you aren't out a lot of money, and it shouldn't be too hard to sell. I wouldn't recommend buying the Lee taper crimp die, as it is included in current Lee die sets, just duplicating what you probably already have.

One other thing - I have used it in reloading 200 grain cast lead semi-wadcutters in .45 ACP, and have had no problems with it, only more reliable feeding than without it. (Edited to add comment re: using with lead bullets)