The front surface of the bolt root has an angle on it. This mates to the angled surface on the rear of the bridge. These two surfaces make up the extraction mechanizm on a Mauser. If either surface is galled it can lead to difficult extraction. If the bolt handle has been welded/replaced, there is a good chance the cam on the root is too soft. Also, if the handle was replaced the cocking cam "V" at the rear of the bolt could be soft. This too can cause hard bolt lift. If cocking after dry firing isn't difficult then look to the former.
If none of these surfaces exhibit galling then setback is a possibility.
While possible, galling is far less likely than setback in a Mauser.
