YOM 1957?

[Matchka]

Is this serno circa 1957? 

[Phosphorus32]

No, it’s a short-lug threaded barrel from 1966. I don’t see an arsenal marking but it could have the last digit Photoshopped out if it’s a Jianshe, or the serial number is complete and it’s from one of the very few arsenals that began production in ‘66.

[Greatguns]

While I agree it's YOM is probably 1966 it is a 1.1M not an 11M so I think it would have come out of one of the lesser factories and not Jiangshe which would put it at the top of the "The Harder Ones" list on the "Dating the Chinese SKS" page in the Guide. Possibly a new SN find for the database???

[running-man]

I would guess a scrubbed and restamped gun personally. Those odd S/N’s with no Arsenal stamps very often are.

One way we can know for certain it’s not ‘57 is of course the short lug as P32 pointed out, but also the sans serif font. Sans serif font didn't come about on T56 S/Ns until 1966. 

[Boris Badinov]

Are all the standard serials present and matching?

[Boris Badinov]

Of the three non-26 arsenals producing the Type56 in 1966, at least one of them is known to have omitted  the Type56 designation (五六式)-- at least, that is, on some of the carbines I've seen.

Perhaps the missing arsenal stamp is of a similar type of omission?

I think the san serif serial font was also used by all three of those tearliest, non-26 arsenals.

[Matchka]

Are all the standard serials present and matching?
Yes.