Don't despair.
Vern's on the right track.
Back when I made spinning wheels and handweaving looms,
For a living,
About 10,000 years ago, I did a lot of silver soldering of steel.
Gotta use a high silver content solder,
Not the hardware store plumbers stuff.
And an acid-etch salve.
Now, you can either find a jeweler or
A smith who knows how to silver solder.
In either case, strip the bolt, because it will get hot
Enough, possibly, to strip the firing pin spring of its temper.
Or you can try it yourself. If you do,
Find a little pencil flame torch,
And read up on silver soldering.
Again, the process will be to take an oversize billet of steel,
Solder it to bolt, and file to fit.
isher