It is a Chinese SKS, made in one of the many many Chinese factories at some point after 1956. Inside the triangle there will be a number such as 26, 36, 6336 or other, that will identify the factory that made it. The very first year production were known as the Sino-Soviets and a SN of a western letter followed by four digits, such as A1234 and were made in 1956 in Jianche factory which is designated Factory 26. After that year (nobody knows exactly when except the Chinese government) several other factories came online and made the SKS. For Factory 26 ONLY you can add the millions digit to 1956 and get the manufacture date, but only for Factory 26. Oher other factories came online sometime after 1956.
The three chinese characters translate roughly to 'Type 56' and it is most likely a refurbished military model with those markings.
If it is not a Triangle 26 and you do not know the date of manufacture there are several things to look at in order to get an idea of the era ....threaded barrels vs pinned, milled trigger groups vs stamped, rear sight markings, blade vs spike bayonet, etc. You can peg it at early, mid or late era with that info.
One good source to learn more is simonov.net
The SKS is generally a great little rifle and lots of fun to shoot.
Cheers
