That crimp groove at the top should be level with the case mouth, then the crimp set to roll the lip of the case mouth into the groove. Whether you need a heavy crimp or a light one depends one how much recoil your load has. A heavy recoiling load can require a heavy crimp to prevent the bullets backing out during firing and jamming rotation of the cylinder. That's why the crimp groove is there. But if you are using a light target load (say, 3 grains of Bullseye) and the gun isn't a flyweight, then a light crimp will usually do, and that extends brass life because it takes more reloading cycles for a light crimp to work the brass to the splitting point.
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