Found this posted by Different on another forum.
Feedback is appreciated. From the 04-29-2012 version of M14 Rifle History and Development:
"Notes On Chinese Parts
USGI and commercial manufacture parts are theoretically interchangeable but occasionally the fit is too tight or too loose between each other. Generally, USGI and commercially manufactured parts are interchangeable with their Chinese counterparts but there are some exceptions. When the select fire Chinese M14 rifles were assembled in the 1960s, the last five or six digits of the receiver were electropenciled on the associated bolt and firing mechanism. Chinese bolts made in 2011 were stamped with a four digit number on the bottom side, e.g., 1223.
Barrel - Chinese barrels have metric dimension barrel shank, gas cylinder lock and suppressor nut threads. However, the Chinese barrel shank thread size is very close to the American made receiver barrel ring thread size. Chinese M14 barrels will usually, but not always, thread into an American made M14 type receiver without any trouble. Nonetheless, barrel installation and headspacing should be performed by a reputable M14 gunsmith. A USGI gas cylinder lock will not fit on a Chinese barrel because of the differing thread sizes. Similarly, the Chinese gas cylinder lock will not fit on a USGI or U. S. commercial manufacture M14 type barrel. Introduced in 2010, gunsmith Barry Jensen, owner of Bits of Pieces (Delta, BC), manufactured a combination gas cylinder lock front sight for Chinese M14 barrels.
Chinese flash suppressor nut-to-USGI barrel - The Chinese flash suppressor nut will go on without resisting but at a slightly downward angle due to the slight difference in threads.
USGI flash suppressor nut-to-Chinese barrel - The USGI and Chinese flash suppressor nuts are interchangeable on the Chinese barrel.
Bolt - For unknown reasons, the Chinese did not use equivalent AISI 8620 alloy steel for their bolts as specified per the USGI drawing but elected to make them out of equivalent AISI 4135 alloy steel. Chinese bolts have austenite and ferrite grain structures with surface hardness varying from 33 to 47 HRC. With thousands of firing cycles, the contact points will peen. If the bolts are heat treated to improve hardness, the hardness increases all the way through the bolt instead of just at the surface. Hardening a Chinese bolt will add a little more service life to the item. In the long term, however, hardening a Chinese bolt is still not desirable. This is because increasing the core hardness of the bolt decreases the core toughness.
Another significant problem plagues Chinese bolts imported into the United States. Besides not being made of a material suitable for long term use, the locking lugs are too narrow. Thus, American and Chinese bolts are not interchangeable except in very rare instances. The owner of a Chinese M14 rifle with a Chinese bolt should not expect a USGI bolt to drop in to the Chinese receiver. Even if a USGI bolt does fit the Chinese receiver, it may headspace less than the safe minimum, 1.630 ", or it may headspace longer than the SAAMI maximum, 1.634 ". Converting a U. S. imported Chinese M14 type rifle to accept an American made bolt should be performed by an experienced M14 gunsmith. These problems may or may not continue to affect Chinese M14 bolts which were more recently exported. For example, three Norinco M305 rifle bolts shipped to Canada in 2003 were tested for surface hardness. The results ranged from a minimum of 45 HRC to 48.5 HRC, with the average at 47 HRC. More detailed information on the bolt material or the core hardness of these 2003 vintage bolts is presently unavailable. Chinese ejector springs tend to run about 1/16 " longer than USGI ejector springs.
Firing Mechanism - The machining of Chinese firing mechanism parts is comparable to USGI firing mechanisms. The Chinese trigger guard is made with the bent tab stop similar to the late version USGI trigger guard. Chinese hammers and triggers are sometimes a little soft, but this can be corrected with appropriate nitrocarburizing treatment. The pin sizes and locations in the Chinese unit are the same as the USGI original. Occasionally, a Chinese hammer pin or trigger pin may be too soft or machined slightly too narrow. The Chinese magazine latch pin is 4 mm diameter, slightly thinner than the USGI pin.
Gas System - Chinese gas cylinders and gas cylinder plugs are made of molybdenum-chromium alloy steel and gas pistons are chromium plated. Chinese and American gas cylinder plugs are not interchangeable. The Chinese gas cylinder plug has 25.4 threads per inch and the USGI gas cylinder plug has 40 threads per inch. The Chinese gas piston outside diameter and the gas cylinder inside diameter are slightly larger than USGI gas piston and gas cylinder drawing specifications. A USGI gas piston may be too narrow to function properly inside a Chinese gas cylinder. The inside diameter of a Chinese operating rod spring is about 0.010 " smaller than a USGI spring. Some National Match operating rod spring guides will not fit inside Chinese operating rod springs because the interior diameter is too small.
Operating Rod - Three kinds of operating rods have been identified on Chinese semi-automatic M14 type rifles. One kind has no notch at all for the connector assembly. Since this version cannot be used with a connector assembly, it is likely post-1978 production. Another has an almost straight angle cut to the notch, which does not closely match the USGI connector’s contours. These operating rods have numbers engraved on them. The notch may have been machined away after original manufacture. The third type of Chinese operating rod has a connector notch very similar to the USGI model, but with a slightly more circular shape. The third type was made in 1965 as part of the production of 100,000 complete rifles. In all other important dimensions, the three types of Chinese operating rods are the same. Chinese operating rods are forged and are as hard as USGI Harrington & Richardson operating rods.
Rear Sight Assembly - Chinese and American rear sight knobs and bases are not interchangeable because the Chinese sight parts have about 36 threads per inch versus 32 threads per inch for the standard USGI rear sight parts. However, a complete Chinese manufacture rear sight assembly will fit on an American made receiver and vice versa. The Chinese rear sight base is a casting.
Stock Assembly - Chinese connector locks were standard length in 1965 production M14 rifles but shortened to sit flush with the receiver in post-1978 production rifles. USGI stocks require some filler material to prevent lateral drift of the shortened Chinese connector lock. Chinese butt plates and butt plate flappers are both made of steel. The butt plate is a casting. The flapper-to-butt plate joint is built up by welding then ground flat. Two types of Chinese M14 butt plate flappers have been observed: Type 1) the flapper has two raised indentations on the right side of the hinge and Type 2) the flapper has one hole on the left side of the hinge as the muzzle is pointed down range. Chinese M14 firing pins have a phosphate coating. Chinese flash suppressors are castings. The bolts and operating rods of Chinese M14 rifles imported in May 2006 into Canada have etched numbers on the bolts and trigger housings and W C E is marked on the elevation knobs."
and
"Table 47: Chinese M14 Rifle Part Markings
Chinese Rifle Part Identifying Marks
barrel KFS and CAI importer markings for Poly Technologies and CAI markings for some Norinco rifles, occasionally a single digit number or letter under the hand guard
bolt may have numbers electro-penciled on the top or bottom
elevation knob counterfeit W C E
flash suppressor electro-penciled or stamped number
hammer no markings
hand guard silver painted bottom with counterfeit DT25
operating rod may have electro-penciled numbers and the connector notch shape is different from USGI design
trigger housing five or six electropenciled numbers
windage knob counterfeit W C E"
