Did You know back in the day , there were re-loaders back in the states that did our rounds , we’d sight in for differences on each lot that came in .
I did not know that, interesting. To get the best accuracy you size the brass for the exact head space for the rifle you are reloading for. If reloading for just general use you have to size the brass small for the cartridge spec. When you size for the exact rifle it is usually from brass fired in that gun that has expanded to exactly fit the chamber. That means there is no movement of the round on firing and the bullet does not slam the barrel from being misaligned.