It depends on case brand. I wrote I use either Winchester-Western or Sellier & Bellot 30-06 brass for reforming and shortening to 9.5x57. On these brands case wall thickness tapers very gradually through wall, shoulder and neck, so no neck turning or reaming is necessary. RWS cases, on the other hand, have a thin neck and a sudden increase to the shoulder. These form a sort of "donut" around the new neck, if the shoulder is set back. Consequently reformed RWS brass would require neck reaming or -turning, so I don't use such brass. Other case brands may be in-between, but I have not tried them, as once-fired S&B 30-06 brass is plentiful on any German range and available for the picking-up.