Shortly after beginning load development in an old 788 in 6mm, I acquired a sweet little custom built on a Model Seven action. Realizing the potential for problems, I checked some brass fired in the 788 and sure enough, it was too tight for the Model Seven. Knowing what to do (which is not the same as doing it right), I adjusted my FL die so that brass fired in the 788 would cycle in the Seven. Evidently, I missed something because a handful of the cartridges I loaded up fit the Seven too tightly and I am all but certain they are the brass that were fired in the 788. I'm not sure how I managed to screw this up but I sure did it.
Fired brass hardens and will need to be sized slightly more due to setback than virgin brass. So when setting up an FL die to size brass fired in a larger chamber to fit a tighter chamber, you need to make sure you're fully sizing the brass, not partial fl sizing. Even then occasionally you'll get fl brass that just doesn't size down enough to fit.
Just buy virgin brass and have dedicated brass for the tight chambered gun. No risk of accidentally having a round that won't chamber at the wrong time, like on a hunt.
