Groove diameter, you mean, I think.

The actual bore diameter is not important when deciding what jacketed diameter bullet to use, but becomes important with cast bullets with bore riding sections.

The normal Euro "bore" diameter for a 9.3, is .358", with a .366" groove diameter - as for the 9.3x62, etc, then .366" is normal for bore diameter for 9.5mm(.375 calibers).

Since the rifle came with a .358" mould casting the .280gr. RN bullet, this sounds like the old Lyman #3589 OBSOLETE mould. If it is, treasure it - it has been obsolete for many decades & it is a wonderful bullet, being a perfect RN shape with long-land bearing surface.