Hi Dumprat,
The mauser action is not meant to be single loaded. I think you can modify the extractor to do this but it is much easier to just press a single round into the magazine and load from there. If it still pushes in front of the extractor from there then you need to modify the floorplate or action rails to suit the larger projectile. You can load from on top of the floorplate by depressing the side of the extractor as you move the bolt forward, however this is not a great practice.
Regards
Les