Its a DB series....there is little known about them that is based in fact...but we sure do speculate about them.
The Chinese character is likely either the city where it was made, or perhaps the city it was issued to.
There is a section in the guide on DBs and DPs that has the city code characters translated....in the Arsenal Stamps section.
Yours appears to be from Lushun City. (pardon me if I am wrong, but it is upside down and early in the AM)
The stock, bipod, magazine and muzzle brake are all aftermarket addons.
Dating these is virtually impossible based on the serial, usually...but for the most part the ones with indicators towards the date point to 70-71ish.
http://chinesesks.weebly.com/arsenal-stamps.htmlyou can also join the fun here:
https://sks-files.com/index.php?topic=1002.0;topicseen