There will be more of the cylindrical mandrel’s length in contact with the brass at any moment both in front of and behind the much narrower contact patch offered by an expander ball of the same diameter.
Keep the .307†ball you've used with good results and then follow with running ‘em over the PMA expander to nudge the neck ID up that last little bit to where you’ll get that .335†neck OD.
Keep the .307†ball you've used with good results and then follow with running ‘em over the PMA expander to nudge the neck ID up that last little bit to where you’ll get that .335†neck OD.
