Interesting Chinese Submachine Gun

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A reader asked for help identifying an interesting Chinese gun I have never come across before. This gun looks remarkably futuristic for a gun that has been around since at least during WWII. I am sure someone here can identify it for us.
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Photo taken in Beijing Military Museum
The gun has a very long receiver and the bolt is obviously not telescopic. Despite being a long gun, the barrel is relatively short, it accounts for less than a third of the overall length! Fire control and magazine release are placed where they can be operated with the hand still on the foregrip, quite a nifty feature.
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Photo published in [Report from Red China](http://www.amazon.com/Report-Red-China-Harrison-Forman/dp/9990381976) by Harrison Forman (1944)
I love the curvy styling of the thumbhole stock in the above photo.