I believe the Soft vs Hard Crimp will mainly apply to the Roll Crimp. The more that you adjust the Crimp Die down, the more crimp that is applied to the shell case in the crimp groove of the bullet. With loads that do not recoil a great deal, you do not need to apply a great deal of crimp (Soft Crimp).
With a round that recoils a great deal, Normally Magnums, you need to apply more crimp than you would with a light recoiling round to prevent the bullet from backing out of the shell case (Hard Crimp). With a revolver you will have 4 or 5 rounds in the cylinder that will experience the bullet pulling force of heavy recoiling rounds being fired. Each round fired will exert force on the remaining rounds in the cylinder. This can lead to a bullet being backed out of the shell case to the extent that it will lock up the cylinder. The same thing can happen in heavy recoiling magazine fed firearms. A consideration, you have a bolt action that holds 5 rounds total in the magazine. You fire a round, and top the gun back off. Do this a few times, and the four rounds that have never been chambered have experienced a lot of bullet pulling recoil.
You are limited to just how much crimp that you can apply by the shell case. At some point increasing the crimp will buckle the shell case.
Soft Crimp: Just enough crimp to keep the bullet in place on a light recoiling round. Does not work the brass a great deal.
Hard Crimp: The crimp die is cranked on down to apply the maximum amount of crimp without buckeling the shell case.
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