I don't know whether Ming Dynasty crossbows have already been discussed.

But I found a link at http://198.66.52.119/images/ming_xbow/ming_xbow.htm containing some info about Ming crossbows. The info seems to be taken from Qing encyclopedia (Gujin Tushu Jicheng 古今图书集成). But the illustrations have yet been translated into English.

Does anyone have more info about Ming crossbows?