Welcome to reloading. Is it absolutely necessary, NO. The 45 ACP is a straight wall case and in most cases does not require a crimp. The Lee pistol dies come in a three die set or the Deluxe 4 die set, which as you know has the Factory Crimp Die included. You can load fine ammo with the three die set.
Now having said that, I always buy the Deluxe 4 die sets for pistol, just because you get the FCD for like $5.00 or so which is a lot cheaper than if you had to buy the die seperately. Is the die useful, yes. There are times you may want to use the FCD just to insure that the case is tight to bullet (just a touch of crimp) and is completely formed around and I beleive the term is concenticly even on all sides. This insures that you will get full power from your load and that there is no leakage around the bullet. Most bullets will fit quite snug and is not a worry, UNLESS you are shooting non-jacketed LEAD bullets. (they are less perfect and require a grease ring around them to insure seal.)
I use the FCD on my 45 ACPs for two reasons, 1st is that it is like a second resizing without the decaping pin to insure my rounds have not been flared too much during the powder drop and are back to spec so I will not have a single falure to feed. (mouth of case being just a bit to big for the chamber).
The second use for the die is actually my first reason for using it, I shoot about 100% range pickups. (cases fired from someone else's gun as well as my own). In combination with the Lee Bulge Buster set, I use the FCD to fully resize all cases (removes any case bulges) and puts the case back to factory spec, before resizing and decaping the case. This also insures that the case will fit your chamber 100% of the time.
So do you need it, no, but it is a handy thing to have around.
Good Shooting and stay safe.
PS: I just read jibjab's post and it reminded me, the 4 die set comes with a carbide resizing die, and I believe the old three die sets did not, so you have to lube the cases. This may have changed since it's been a long time since I have purchased any new die sets.
Si vis pacem, para bellum
Last edited by Jim243; June 24, 2011 at 10:46 PM.