Charlie wrote: ... I like the Lee FCD's so I'm going to end up with one of those regardless.
Charlie-
Perhaps you already know the following. I think I've got the details described correctly; if not, I hope that you or other forum members will correct me.
The Lee 45-70 Factory Crimp Die, modified for use with the 450B cartridge, is used differently than FCDs in other cartridges. As you know, most Lee FCDs are designed with an internally-ridged collet either to mash the mouth of the case into a bullet's cannelure, or simply to squeeze the mouth so hard against the bullet that a surrogate cannelure may be formed.
This mashing technique cannot be used with some revolver and auto pistol cartridges. So Lee makes two other types of dies they also call "Factory Crimp Dies", but which operate with a completely different, non-collet mechanism.
One of these is for straight-sided revolver cartridges like the 38 Special, 357 Mag, 41 Mag, 44 Special, 44 Mag, 45 Colt, etc. The Lee FCD for these cartridges are manufactured with a floating internal sleeve. When a cartridge is run up into the die, the sleeve will apply a roll crimp turning the case mouth into the bullet which should be either of lead, or made with a cannelure into which the crimp is pressed. The sleeve is adjustable for the location of the roll crimp. The die also is made with a carbide insert at the mouth of the die to ensure that the case diameter is correct.
The second type of non-collet Lee FCD is made and used similarly, except that the floating internal sleeve applies a taper crimp. This die has been made for auto-pistol cartridges including 9mm Luger, 380 Auto, 38 Super, 40 S&W, 45 ACP, etc.
All of these headspace on the mouth of the cartridge. Neither a roll crimp nor a "mash" crimp can be applied without the possibility of causing headspace problems.
The 450B resembles auto pistol cartridges because it headspaces on the case mouth, and a taper crimp is needed. The Lee FCD that applies a taper crimp to the 45 auto-pistol cartridges cannot be used because the carbide insert is too small in diameter. (I wrote a post about this that's now a sticky:
A Note on the Lee 45 Carbide Factory Crimp Die #90864).
The Lee 45-70 FCD is designed to mash the 45-70 case mouth against the .458 bullet, and cannot be used to perform that action with the 450B. If suitably modified, it can be used to apply a
side-crimp, mashing the case wall
below the mouth into the side of the bullet. This retains the headspace dimension of the case mouth, while increasing bullet pull.
Lee also makes an uncataloged 45 Colt FCD that uses the usual collet-with-a-ridge to apply a mash-type crimp to the mouth of the rimmed 45 Colt cartridge. As described in a couple of threads on the forum, this die can be used to apply a side crimp to the 450B cartridge. It should not be used to apply a crimp at the mouth of the 450B case.
For the most part, side crimps with the FCD are not routinely applied during reloading. The Hornady taper crimp die works well. However, for solving some problems with initial powder ignition, the side-crimp can be useful. This occurs particularly with use of light bullets.
Unless and until you encounter such problems, use of a side-crimp applied with a FCD is not necessary.
Again if you knew all this, then my apologies for the long post and for sucking the energy out of billions and billions of helpless electrons.
--Bob