Let me quote my post from another forum about the type of crimp used for big bore heavies:
I really like the uncataloged Lee FC collet type die the best. For J word boolits, they wouldn't really need to be modified but for cast where it is critical that the driving band of the boolit remain as sized by the sizing die, I modify mine for a narrower crimp band and I also shorten it so it brings the crimp band down on the case. Let me see if I can get some photos to post.
Stock unmodified collet from the FC die:
Stock unmodified collet showing placement of the crimp band on a .45 Colt brass:
Modified collet showing the narrower crimp band by shortening the top of the collet:
Modified collet showing crimp band lowered onto the case mouth by shortening bottom of collet:
Beartooth 340gr and 325gr GC boolits after using the modified crimp:
Lee 452-300 GC mold 320gr boolits after using the modified crimp:
300gr Speer "Deep Curl" on left, Buffalo Bore "Deer Grenade" on right, notice how the crimp band swages into the cast boolit a little smoother than the more sharper band on the Speer boolit that is crimped into the cannelure. The Deep Curl on the left was done with the modified crimp die.
(EDIT: The Buffalo Bore "Deer Grenade" on the right is a factory loaded round from Buffalo Bore, as you can see they use the same collet crimp but I think theirs is likely unmodified):
Last pic, Hornady 300gr XTP-MAG on left, Speer "Deep Curl" on right, after using the modified crimp die:
Sorry for writing an essay but I saw that using the collet style die as manufactured by Lee was great for jacketed bullets, but needed a little adjusting to work at it's best on cast. So far the results have been very consistent, I am sure this crimp shortens the life of the brass but it out performs a roll crimp by a long shot. In a heavy recoiling gun like the .454, this crimp wins hands down. I shoot the boolits shown with heavy loads of H110 in my old Vaquero and I cannot see any movement at all of the loaded boolits in adjacent chambers. In addition to this crimp, it is very important to have good case neck tension. Of all the crimp styles to choose from, this is the only style of crimp that only squeezes from the sides of the case mouth and does not press down or in on the seated boolit. I hope this information is of some use, it is working like a champ for me!
