I see. From what Jliu said 哈: 哈尔滨 is (Harbin City). However, it's my understanding that Chinese symbology is very precise. (I may wrong though), so in considering that precision the first character her in front of the colon interprets as WHAT: So the entire glyph interprets as - what: Harbin.... It doesn't specify that Harbin is a city, town, or whatever they may be called in china. So, just maybe, Harbin is a region? Like a county (or their provinces) with Harbin City within it's boundary's?
The reason I think this is because if these rifles are destined for other country's they really didn't want to give away precise arsenal locations. Therefore, no markings to signify arsenal or location it was built.
However, the bigger picture would possibly prove that theory wrong since battlefield pickups would have the arsenal stamped in them.
Just shootin spitballs at the wall.
Regardless, China has been around much longer than most governments. They've through so many reconstructions only they know can keep track. Which brings me back to them possibly using older out-of-date and out of use symbology for stamping some rifles and not others?