1. take rifle to range
2. set the firing pin to stick out from the bolt face slightly (a bit over .050" 'by eye').
3. chamber a round
4. aim the rifle downrange
5. pull the trigger.
One of two things will happen, either the rifle will fire, or it won't.
Result 'A': The rifle fires, and continues to do so with subsequent rounds. You are good to go.
Result 'B': If the rifle does NOT fire,
* wait a minute before opening the bolt to eliminate the possibility of a hangfire.
* Remove and disassemble the bolt and screw the firing pin 'in' a half-turn.
* reassemble the bolt and reinstall in rifle.
* repeat steps 3, 4, and 5 and 'B'until you consistently get Result 'A'.
Then, take a mental note of the relative positions of the end of the firing pin relative to the back end of the cocking piece for future reference.
I had to do this with a REALLY rough, ugly, but complete 1945 Ishevsk M44 I bought as a parts gun about 10 years ago for $35. Fairly good bore, but it shoots WAY to the left of the sights.
Didn't have a protrusion tool with me at the time. The firing pin adjustment, and the first several shots from that rifle, were made by tying the rifle to a bench and pulling the trigger with a string. After I finally doped out what it took to get the rifle to feed from the magazine (it wouldn't when I bought it), I decided to not make a parts gun out of it after all.
I STILL don't have one of those handy-dandy combination protrusion gauge/screwdriver thingies, although I DO have one of the screwdrivers WITHOUT the notches.