Thanks for answering my questions, wogpotter.
On your progressive press, if you have enough die stations, you lose nothing by using the separate crimping die. The Lee FCD should not be necessary for plated or jacketed rounds, as they are rarely oversized enough to bulge the case and make chambering difficult. So, a spare seat/crimp die with the seating stem removed would as a "crimping die" just about as well as any manufacturer's dedicated crimping die (e.g. Redding's excellent profile crimp die) or Lee's FCD with or without the post-sizing ring removed.
drail and buck460XVR are exactly right about the bullet pull forces for plated bullets. Plated bullets are not driven to the power levels that jacketed bullets can be, nor normally used with the powders that require the high "start" pressures like H110.
Note that since you want a taper crimp on your plated bullets and as buck460XVR suggested you can get taper crimp with a roll crimping die. But you MUST have it finely adjusted. For that fine an adjustment, all your cartridge cases MUST be the same length. So case trimming will probably be necessary. Fortunately, it won't be necessary very often.
I should, at this point, tell you that if you have the combination seat/crimp die's installation adjusted properly (this is not as easy as adjusting two separate dies, but really, not all that hard) you really do not need to separate the operations. But since you have decided to go with the dedicated dies, I will say no more about it.
As mikld mentioned, you can taper crimp revolver rounds with no worries, particularly for non-magnum power levels. If you happen to want a roll crimp on bullets with no crimp cannelure/groove, it is possible, by seating the bullet deeply enough, to roll a crimp over the bullet's ogive. IF YOU DO THIS, you will probably be reducing the overall length of the cartridge under suggested limits for the .357 Magnum.
This puts you into uncharted territory. But since you are loading .357 Magnum cartridges, you can consult 38 Special load data to decide if you are inviting dangerous pressures.
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Originally Posted by m&p45acp10+1
Taper crimping is just removing the flare of the case to where the round will chamber.
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And, for cartridges that headspace on the case mouth, leaving the mouth able to butt up against the headspacing shoulder at the end of the chamber.
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Originally Posted by m&p45acp10+1
Roll crimping rolls the lip of the brass into a cannulure or grove to give a little extra hold to the bullet. It helps slower burning magnum powders to build pressure as has been stated. It also helps to keep the recoil of the gun from acting like a kinetic bullet puller on the rest of the chambered rounds.
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Well put.
So, short answer:
If you are willing to trim your occasionally to ensure they are all the same length, a single roll crimping die will do for both the jacketed and the plated bullets. If you don't mind having an extra die, using the taper crimp die for plated and low to medium power jacketed loading and the roll crimp die for jacketed high-power loading. I don't know how difficult it will be to find a taper crimp die for .357 cartridges. Most will be roll crimp. I believe Lee Precision will make one for you, though, reasonably priced.
Using the Lee FCD vs any other manufacturer's crimp die or even making your own (roll crimp die) by taking the seating stem out of a combination seat/crimp die is likely to make no difference. Finding a combination seat/crimp die for a revolver round that gives a taper crimp is unlikely.
Lost Sheep