I hope you have informed Lee of their design and marketing errors, as they advertise and sell the FCD to "post-size" the cartridge, not as a standard resizing die with a crimping feature. Unless I'm misreading you, you're suggesting the proper procedure for using an FCD is to prime and charge a fired, not-resized case, set a bullet atop the case, seat the bullet to the desired COL and then run the cartridge through the FCD to resize it from it's fired size to factory spec while at the same time applying a crimp. I'm curious how you get a bullet to not slip into a case that has been fired and not resized until it hits the FCD.
Apparently you've never tried to put a .451" jacketed bullet into fired 45acp cases. You wouldn't be so curious and would actually have 1st hand knowledge on what works and why.
Here's 10 random r-p 45acp cases I pulled out of a container of range puck-up 45acp brass. The brass is not sized/cleaned/nada. Simply picked up out of the dirt and tossed into a container. I have no idea when these were collected or what firearms they were shot out of. I can say it's been slim pickins this year with the ammo/reloading components shortages going on. It took 6 months to fill a coffee container 1/2 full/ 20+ range trips.
2 of the r-p cases would accept the .451" jacketed bullet and easily held it tight enough to hold the bullet in place. (2 bullets on left)
6 of the r-p cases would barely accept the .451" jacketed bullets holding onto them but as you can see the bullets are crooked. (4 showing and 2 turned to read the r-p head stamps)
The 2 upside down r-p cases on the right would not allow a .451" bullet into their case mouths.
Anyway that 10 un-sized r-p 45acp cases with 2 of them able to start a bullet strait along with having the ability to hold onto the bullet/take force to seat the bullet. 6 of the r-p 45acp un-sized cases were too tight and would not allow the .451" jacketed bullet to start strait. 2 r-p 45ACP UN-SIZED cases were to tight to allow the .451" jacketed bullet to even start.
You really should do some re-reading and testing for yourself.
I understand it's a heck of a lot easier to sit in front of a keyboard and type. But there's this thing called "sweat equity". If you put in the sweat equity you will rewarded/rich in knowledge. And not have to rely on other or question what others (including people like ED Harris) are actually doing.