if you crimp too much, the cartridge will go in too far when chambered.
This should be impossible with the Lee FC die as it will not reduce the case mouth dimension further than minimum SAAMI dimension and the post sizing ring only reduces the case to the maximum allowable SAAMI diameter if its bulged during seating.
To adjust the FC die properly:
1.First back out the crimping adjustment on the top of the die several turns and back out the lock ring on the die body. The sleave on top is what applies the crimp on the case on the pistol dies not a shoulder in the die body like a regular crimp and seating die.
2. With the shelholder in your press bring up the ram fully to the top.
3. Screw in the die and adjust so that the bottom of the die is just a hair higher than the top of the shell holder, just like you adjust a full length sizing die. Lock the position with the locking ring.
4. Insert a loaded round with the bullet seated and run it into the die. The crimping adjustment should be out enough so that no crimp will be applied.
5. With the round in the die and the ram at the top of it travel screw in the crimping adjustment until it contacts the case mouth.
6. Back out the case a bit and turn the crimp adjustment a half turn down then bring the ram up to add crimp. Lower the round and examine the crimp you just made on the case. Turn in the adjustment a bit more in for heavier crimp and back it out for lighter.