If it smooths out a bulge in the case then it WILL swage down the boolit. If the brass case diameter is reduced aka smoothing out the bulge then lead has to be displaced physics won't be denied. Two things can't occupy the same space at the same time. The only question is how much the swagging down effects accuracy in the gun you are using.
Simply measuring a pulled bullet will tell you how much it has been swagged down. Incidentally we talking about the FCD for pistol cartridges not the FCD Lee makes for rifle calibers. The two aren't the same.
Take Care
Bob