Steve:
Pull off the norinco stock and look at the front face of the stock ferrule. I'll bet you see finish wear there. The front face of your stock ferrule is not supposed to rub against the stock band (the sheet metal thing being the gas cylinder with a lip for your stock).
Every norinco plastic stock I see is running against the band. This is hurting how your rifle shoots, I guarantee it.
The fix is to set back the ferrule a couple mm so it is not pressing on the gas system parallel to the bore, or to use another stock.
You can remove the ferrule, carefully file back the shoulder and remove some plastic off the tip, then epoxy the ferrule back on. When I can't convince someone to buy a better stock, that is the repair I recommend. It makes the stock work as intended, but a plastic stock will never be as rigid as a usgi stock.
They make good beater stocks though.