When the M98 was designed for COO, the rear of the bolt body was thicken to provide a wide spiral cut cocking ramp to lessen the risk of galling and premature cocking ramp wear. Something to consider when converting a COC bolt to COO.
See pg 100 of Jerry Kuhnhausen's The Mauser Bolt Actions, a shop manual for more technical/mechanical details on why he does not recommend the conversion.
