Didn't get an answer about how the OP was crimping prior to looking at a taper crimp or a Lee FCD?
I would guess, and it is only a guess, that the OP was seating the bullet and crimping in the same step. This can cause some case/bullet/COL/crimp to conflict and it could put a bulge in the case.
It is always best to separate the two actions.
Next, if using jacketed bullets and cases that have a nich chamfer, it is possible to seat the bullets without having any flare/bell on the case mouth. This also can cause problems with come combination of components.
If your case are sized properly and you have sufficient case mouth flare and your expander has increased the case ID to 0.001-0.002" less than bullet diameter, the Lee FCD will not even touch the case with the carbide insert. It just touches any part of the case that exceeds SAAMI max case diameter.
In many cases (particularly hot 9x19 and .40S&W), the fired case will have a slight bulge. This bulge can cause a raised ridge to form down near the extractor groove of the case and cause a failure to chamber. The best solution to this is, if you notice this ridge, to run your cases through the Lee Bulge Buster so the ridge never has a chance to form.
Also, if you can easily feel or see the case bulge, that case has been weakened enough that I dispose of them.
Lee makes an excellent taper crimp die, along with their FCD.