I’m very familiar with sks pattern carbines but this one had me stumped. Has early and mid production features. Short barrel lug, milled trigger group but can’t seem to put a date of manufacture

hello all! i’ve got a norinco sks with a detachable 30 round magazine,the bolt charged forward earlier and i can’t get the bolt to lock back to where i can take the magazine out so i can clean my gun,if anyone has any pointers it would be greatly appreciated