Most Mauser actions are just mild steel, so the welding part really wouldn't be tough. It could be welded with literally any kind of welding process because since you don't have to control the heat because everything will have to be re-heat treated. So the actual welding is easy.
Making the fixture to do the welding is where you run into money. You will need a custom heat sink to run down the center of the two pieces to keep everything concentric, and to minimize warping...there is always warping when you weld steel. Then after the weld, there will be a good deal of file work to make sure the bolt still slides easy, and the outside all blends in.
Then you have to do the bolt. Same thing, you want a fixture that will keep warping to an absolute minimum.
And of course, all will have to be re-heat treated when done.
Would be a cool project, but it wouldn't be cheap. I know a gent who could do it, but it would depend on if he has the time.
I think I could do it, but I'd rather practice on one of my guns than practice on a customer's gun.
