The oversize expander ball creates a false shoulder. (338 might be too big.) You would expand the neck (annealed brass and lots of lube), Then go back with the 308 sizer and work down the neck in small increments until the case will chamber. Do all of your brass this way. Load and fire form. The shoulder will move forward. Then you have to set your die up for the new case head space length. Only bumping the shoulder .001" - 002" back .