I think it has to do with how far the firing pin sear is held back by the trigger, if you get some wear it is not held far enough back and the slot in the firing pin does not line up with the pin on the safety shaft and will not turn. When you press the trigger and take up the first stage it pushes ...

I have a Mexican Mauser. It is 7mm and is a model 1910 and is of Mexican maufacture. They were made up to and including 1934. They are a small ring type 98. Hope this helps some. I am looking for a new 7mm barrel. Does anyone have a clue? The barrel is 29" long.