The two photos either side of that showing the leade and rifling in the barrel are showing the feed ramp which appears to have been severely cut away when the action has been opened up for the longer cartridge. Is there anything left of the feed ramp for the lower bolt lug to lock up against?
Is a common enough process opening up M98 actions for longer cartridges, I have one myself in 404J and there is a bit of work required on the feed ramp to fit longer cartridges but if what the photos show of the feed ramp on your Mauser is what it seems, that is quite radical and I'd be a bit concerned that the action strength has been compromised somewhat.