The firing pin itself can be made from a headed decapping pin or even a common nail. To keep it from falling out of the slot in the bolt when the striker is cocked, a simple U-shaped plastic holder is needed. Nylon is good material, but even a piece of shotshell will do. The pin should be a friction-fit in the holder.
The firing pin should be trimmed so it protrudes about .050" from the bolt face when its head is resting on the uncocked striker (with the bolt assembled). Put a nicely-polished hemispherical working end on it like any other centerfire pin.
Although the .348 Win. rim is slightly undersized, cases work OK and headspace is acceptable. I've fired a lot of them in Vetterli and Peabody rifles with no problems. Buffalo Arms can provide formed cases or it's not difficult to make them yourself.
1. .348 case re-formed. (Some chambers need bases filed/turned slightly smaller.)
2. Excess sawed off and trimmed to 1.5".
3. Loaded with common .44 revolver bullet.
4. 45/70 brass is pretty undersized at the base.
Short pistol bullets won't feed from the magazine. Longer bullets or longer cases are needed for that. Overall length of 2.2", flat-nose, and good crimp are critical for magazine use.
Bullets about 310 grains with a charge of 19.5 grains of SR4759 approximate the original load and will shoot near the sight graduations at 200 yards and beyond. For shorter ranges, a detachable wire sight extension is helpful.
Adjust windage by bending at "A"