[Sport45]

The Lee Factory Crimp Die has a carbide sizing ring at the base. It will post size the brass after you have seated and crimped the bullet (the brass has to come back down through the carbide ring after crimping. This carbide ring is slightly larger than the ring in my Lee sizing die and probably doesn't even touch most of the brass I load. But if the cartridge will pass through the crimp die it will chamber in your handgun. (Unless it is just too long, the FCD can't do anything about that.) The FCD is installed in the press touching the shell holder at the top of the stroke, same as the sizing die. There's and adjustable mandrel on top to set the amount of crimp desired. I use mine to roll crimp revolver cartridges, and barely touch my .45acp and 9mm cartridges. I allow the seating die to take care of the taper crimp in those and really only use the FCD as a final sizing check.

The above refers to FCD for pistol cartridges. The FCD for bottleneck rifle cartridges is a completely different animal.

A case gauge is a good suggestion. For auto pistol I just us a barrel removed from the gun for drop-in testing. For revolver, your cylinder makes a great gauge as you have discovered.