I have noticed on a few 7.62 gas systems of late that there chamber can fit nork pistons. Not all do though. There for if you have sloppy fitting piston you will not have proper vaccum preasure for the gas system to operate properly. Try the piston test and report back.Satain, what makes you think it's the piston? More info please.
Piston drop test - check.
Two options to increase gas would seem to be:
1- enlarge top gas hole in piston.
2- enlarge interior dimension of gas plug.
Due to a number of people posting feeding problems with Norc ammo, particularly with chopped M14s, I won't go and change anything yet.
There is your culpurtright there. Loss of gas preasure at the spindal value coninsiding with the lower preasure Nork ammo and bingo. Some times it pays just to use the stock parts that the Nork comes with instead of mix matching them with US parts just to say it is a US part. Like I always say if it anit broke don't fix it.I took my chopped Norc out again and blasted through over 130 Norinco rounds with only 1 failure to strip the round out of the mag. I had added only a small amount of lube, but perhaps it helped.
I did notice one difference between my stock Norc gas system and the 7.62 system that I added when I had the barrel chopped. The spindle valve was rock solid tight in the Norc gas cylinder, but now that it is in my new US made cylinder, it is so loose that I can move it with my finder. Gas residue around the spindle valve shows that some gas has been escaping. Perhaps this slight loss of pressure is to blame. I will replace the spindle valve just to be sure.
I don't think that I will have to do any further alterations to my gun. Enough people have had the same issues with Norinco ammo, so I'm going to go with that for now.