John Lee, president of Lee Precision emailed me years back when we had THR discussions on the FCD and the bulge buster kits that use the FCD (No bulge buster kit for 9mm as it is a tapered case and cannot be push-through resized with FCD).
He stated the FCD was meant to be used with jacketed diameter bullets to bring out-of-spec finished rounds to SAAMI specs to work with any SAAMI spec chambers. (IMO, FCD is a good tool to fix rounds and the original intent by the maker for straight walled semi-auto pistol calibers). But using FCD with oversized bullets was not the intent of the FCD as post sizing would reduce bullet diameter.
And if bullet diameter is reduced, brass spring back could reduce neck tension and increase bullet setback which would increase chamber pressure.
To all those using FCD, make some rounds WITHOUT the FCD and see what the finished round dimensions are and whether they will pass the chamber gauge.
If they pass, then you are good to go.
If they fail but pass the barrel, then you are still good to go for YOUR pistol.
If they don't pass the barrel, then you got some work to do or you can keep things as they are, it's a free country ... carry on but I would check the finished rounds for bullet setback by feeding/chambering rounds from the magazine. If the slide slamming the bullet nose on the feed ramp does not decrease the OAL/COL significantly, you are good to go.
If you measure significant OAL/COL reduction, you got issues that need to be addressed - we do see threads with "Funny thing happened at the range today" titles from time to time.
Be safe, especially if you are reloading at near max/max charges.