If you were to measure close, new -vs- fully fire formed, and sized as you plan, you would see that all dimensions have changed. This affects capacity directly.
Along with this, the brass grain length has changed(affecting hardness), and clearances have changed. Combined, there will be a difference in the pressure curve rise, given different energy use to fill the chamber with your brass(far more 'contained' at that point). So don't bother load development with all this changing. Take your brass to stable first.
Where a cartridge is small to mid size capacity, with a fastest powder that fills the case, most of a target result/barrel timing was influenced within the pressure peak.
With bigger to overbore cartridges, the pressure peak itself contributes less & less to target results. More slower powder.