The cause may be one or a combination of thngs. You need to check the following:
The problem is usually gunk in the firing pin raceway, on the bolt face, or breech face. Clean, clean, clean!
-Examine a shell that's been fired or a round that failed to fire. Is the pin strike deep and located just below the fold of the rim? If not, is it wide and very long? It could be too big, spreading the energy over too wide an area. If so, hone, or carefully grind the pin to produce a narrower strike and grind a bit off the top, so it doesn't contact the fold of the shell.
-Is there excessive vertical movement of the pin in it's most forward position? If so, get a cold chisel and a heavy hammer and deepen the stake marks in the top of the bolt until vertical pin movement is only a few thousanths when fully forward.
-Is the action and firing pin raceway clean and dry? Gunk accumulates around the firing pin, creating frictioin and sapping energy.
-Is the hammer strut clean and without burrs? If not, clean and hone the sharp edges.
-Does the hammer spring seem weak (compare with other 10-22s)? If so, replace.
Picher