They say one picture is worth....
Pictured below is a Lee FCD (Factory Crimp Die) which is fully disassembled. As can be seen there isn't much to these dies. Left to Right is the locking nut, the die body, the die collet and a 45-70 cartridge loaded with a 405 grain soft point bullet.
When assembled with the collet in the die body, the collet will extend below the bottom of the die body and will have about .125" free travel. That .125" is free play before the die engages a gradual step step in the die body. Holding the assembled die upright the collet can be bumped with a finger and the free travel observed.
The following image shows the cartridge inserted into the collet. The cartridge can only go so far till the cartridge rim stops it.
Note where the brass tops out at the collet. There is no adjustment to a die like this. When the die is placed n the press the ram is run up full stroke and the die is screwed down till the collet bumps the shell holder and the free travel is taken up. The ram is lowered and the die given another 1/4 turn. That 1/4 turn is only for the cam over of the press. You are not really changing anything as to where the collet will squeeze on the case mouth. However, if the case is too short, as can be seen, nothing will happen.
This is the major problem with dies using this design. They rely on the length of the brass and the brass, assuming long enough, must be uniform from case to case in length. If the brass is too short, even by a few thousandths you get zero crimp.
Note: My bad in that I did not include a shell holder which may have made things look better. However, I am sure you get the idea of how this animal works.
Ron
