Almost all of the [ old and new ] Chinese Norc & Poly M14s that I have personally inspected had perfectly dimensioned receivers, as good as the GI genuine M14 receivers I've checked.
HOWEVER,
??some how ??? a large percentage of these old/early Chinese 14s were fitted with barrels that were out of spec with regards to the barrel threading at the shoulder, AND POSSIBLY WITH THE CHAMBER DIMENSIONS TOO LONG AS WELL.
Simply put,
these barrels WERE MACHINED WITH THE SHOULDER APPROXIMATELY .010" TOO FAR FORWARD, AND ?POSSIBLY? WITH AN EXTRA .010 OF HEAD SPACE.
What happens when these barrels are threaded into a correctly dimensioned receiver, is that the rear face of the barrel THEN PROTRUDES ABOUT .010" TOO FAR INTO THE RECEIVER.
One solution , NOT THE BEST SOLUTION , but the one the Chinese went for, was to grind approximately .010" off of the back lugs of the Chinese bolts. [ and I use the word approximately here because it looks like most of these were done by hand, with no real dimensional control except the ol' MARK 1 EYEBALL ].
SO, if you have a OUT OF SPEC Chinese barrel like this, fitting an IN SPEC, PROPERLY DIMENSIONED GI BOLT into your ON SPEC CHINESE RECEIVER, can be a VERY involved process.
Usually it will be much better, to simply thread in a GI barrel instead, and THEN try the GI bolt for fit.
A decent GI barrel and GI bolt on MOST Chinese receivers will USUALLY bring you very close to .308 GO, or perhaps if using a NEW set, a couple of thou short. I've done dozens of these, and IMHO, if you have to lap for more than 15 minutes, you should be using different bolt/barrel combinations.
Which is why, when I did my last batch of GI bolt & barrel conversions, I had SEVERAL different bolts and barrels on hand to juggle with, till almost all of that entire batch ended up with near perfect headspace, full bolt lug engagement, and all done with a minimum of lapping
YPMMV,
BUT
I've BTDT a lot of times,
got I've got the Tshirt,
LAZ 1
[;{)
Hope this helps????
