factory crimp question

Lee's FCD (Factory Crimp Die) performs two functions. Crimping and post-sizing. The two operations are independent of one another and cometimes work at cross-purposes. With lead bullets, sometimes the post-sizing reduces the grip the case has on the bullet. The grip the case has on the bullet is important for three reasons.

1) It keeps the bullet from being knocked deeper into the case during handling and very important, during feeding. This is most significant in autoloaders

2) It keeps the bullet from being pulled out of the case during handling, and very important, during recoil of its brother rounds. This is most significant in revolvers.

3) It keeps the bullet from moving out of the case until a threshold of pressure has been reached. This is most significant with slow powders, but important with all powders.

In taper-crimped cartridges, the bullet tension (the grip the case has on the bullet) is provided by friction more than by crimp. If you post-size a case onto a lead bullet, the case springs back more than the lead does, reducing bullet tension. This is less problematic with jacketed bullets than with lead, but can occur with either.

If your dies are adjusted correctly, the Lee FCD will NOT post-size your loaded cartridges. You will be able to tell if it is by carefully feeling the resistance as you run the cartridge into and out of the die.

The main reason for the existence of a crimp die that operates separate from the (usual) seat/crimp combination die is to simplify installing and adjusting those dies and to prevent the case mouth from digging into the sides of bullet as it is being seated. (This can happen with a strong crimp - mainly roll crimp - on a bullet while it is still being pushed deeper into the case by the seating plug. This is virtually unavoidable with the combo die, but if it is moderate presents no problem.)

I suggest reading these threads:

Not necessary 99% of the time, but convenient.

Lee Precision's thoughts on the matter can be found in these threads:

One thread contains a lively discussion of the FCD and the function of the post-sizing carbide ring in the FCD. The phrase "9mm" is in the thread title, but don't let that dissuade you. It contains responses direct from Lee Precision, too. Read the whole thing. It is worth it.
http://thefiringline.com/forums/showthread.php?t=465091

this thread contains a poll

http://thefiringline.com/forums/showthread.php?t=465603

The Virtue and the Vice
http://thefiringline.com/forums/showthread.php?t=509934
http://www.thehighroad.org/showthread.php?t=691050
http://www.rugerforum.com/phpBB3/vie...?f=11&t=168362
http://rugerforum.net/reloading/6586...tml#post814465

Lost Sheep

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