The FCD has a sizing ring in the mouth of the die and will size the cartridge to the diameter it thinks it should be. I have tried an FCD on cast lead bullet handloads and yes, it did resize my handloads down and resulted in under size cast bullets. Lesson learned, besides, I have been reloading for quite some time and never had a need to resize any handloads, post crimping, revolver or semi-auto. I don't shoot in competition but I've never had a need ti insure each and every round chambered correctly, but then again I never needed to as 99.9% of my handloads will chamber trouble free. Having been cruising reloading forums I quite often see new reloaders having problems using an FCD, but my biggest complaint is "seasoned" reloader telling a new reloader to use an FCD to "cure" their bulging/chambering problems. (kinda like telling a new driver/car owner to just add more water to a leaky radiator rather than fixing the leak). Actually I don't care what tools reloaders use but a pet peeve of mine is telling a new, inexperienced reloader to just hide the problem and not find out why there is a problem and fix it...
I doubt is deeper seating when crimping is from an FCD, but I don't have any of your reloads in my and I can't see what you are doing. The resizing feature of an FCD should not change OAL. Overcrimping can push a bullet deeper though...