The shape of the "barrel neck" (the taper area between barrel and receiver) indicates the upper was either a late prewar or wartime production. It's not impossible to renumber a 7,63 barrel and install it on a "Red 9" frame. Could you post pix of the muzzle, chamber & magazine follower (with bolt open)?
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Most C96s imported from China have 'shot-out' or poor bores. Those C96s played the role of regular infantry weapons (instead of sidearms) in the environment lacking artillery and machine guns. Heavy usage + very poor maintenance + corrosive ammo contributed to what we see today. There are many C96s preserved in excellent shape in the U.S., most of them were old commercial (in this context, civilian) guns. Private property has always been taking care of better

Unfortunately, Schnellfeuer is very rare in the States.