I'm assuming the case you inserted in the chamber is a 22/250 (28 degree shoulder angle) The 6XC has a 30degree shoulder. Not a huge difference but enough to cause the hd space gauge and the 22/250 case to contact @ different datum points & give dis-similar readings/ depth in the chamber. A cartridge HD space gauge insert for a Hornady Comparator is in order here........ Depending on the Mfg. of your F/L die, sizing an unfired case could reduce your CARTRIDGE HD space by as much as .007" to .008" or more compared to a PROPERLY chambered bbl. The folks @ Hornady can tell you if they have a proper cartridge HD space gauge for your cartridge. David Tubb can be reached @ 806-323-9488. I'd put a LOT of faith on his input. He wants the 6XC to succeed!!!! He might have ideas for the cartridge HD space gauge also. I'm sure NorCals idea will work. But why alter the design of the cartridge & give up case capacity to boot ??? Dale