So my Chinese SKS (Norinco marked "Sporter" late model) was popping primers like every 1 of 4 rounds, and a firing pin swap didn't fix it (in fact that replacement pin didn't fit as well and resulted in a slam fire).
So even though I couldn't really see one on the bolt face I thought I'd try the Murray's fix to the "volcano" raised edge around the firing pin hole. Got a 1/2" 82 deg. countersink, and the small fine grit polishing stone that came with my Dremel. Ran the stone across the bolt face a few times (maybe a dozen?) and spun the countersink bit in the hole with just hand pressure about 6 times around, then gave the bolt face a once or twice over with a fine polishing emery board. Also totally scrubbed out the firing pin channel with a .17 brass bore brush and Hoppes followed by Break Free Blast. Put back in the original pin, and it is shaking loosely.
Took it to range and ran 50 rounds through (40 Wolf or Tula steel case and 10 Yugo surplus brass) with ZERO popped primes and no slam fires. Was VERY pleased that this seemed to fix the problem. Was about to order the Murray's spring firing pin but if this fix sticks then I guess it doesn't need one.