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Is There a Real Difference in Crimp Dies?

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Based on some discussion about the Lee FCD in another thread, I need some education please.

Can someone to explain how the dies below differ in crimping for pistol ammo. I currently use the Lee FCD (with the knob on top) and set the crimp so the line on the bullet (if pulled) is almost non-existent.
  • Lee FCD (the one with the knob on top)
  • Dillon Crimp Die
  1. Do these crimp in different ways?
  2. Does one provide better accuracy over the other?
  3. I've seen in different posts that you should have no line, or barely a line around the bullet from the crimp. Is this true no matter what crimp die you use?
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In a pistol, no. And it's not really a crimp at all, but rather a de-bell step which is just enough to take the bell off from the powder thru die. The crimp does not hold the bullet in place, it's the interference fit between the bullet OD and the case ID. Over crimping can lead to bullet setback.
 

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For semi auto cases, especially 9mm, it is TRUE. Putting a bullet in a fired (un-sized) case makes no sense. It is not the correct ID diameter to provide an interference fit. So try this, load some 9mm without a crimp and shoot them in a S&W revolver. It doesn't need to be de-belled (crimped) because it does not sit in a chamber. The less taper in a semi auto, the less sensitive the round is to de-bell, such as a 10mm or 40S&W at .002" per side versus a 9mm, at .0055" per side.
 
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