It's much easier to get a replacement part; they cost about $12 at VTI Gun Parts (I'm assuming a Walker bolt will work). It will likely be a bit oversize and require some polishing to get perfect, but that's gotta be easier than welding more material on a small, thin, curved piece of metal. And I think silver solder will not be hard enough to last in that application. The mating surfaces of the bolt and hammer need to be fairly hard to withstand wear. That's probably the reason yours is worn out; many older Italian repros had action parts that were not sufficiently hardened. So did the originals, BTW.
