M1895 Nagant
One of the mechanically interesting guns that is really widely available in the US for a great price (or was until very recently, it seems) is the Russian M1895 Nagant revolver. It was adopted by the Imperial Russian government in 1895 (replacing the Smith & Wesson No.3 as service revolver), and would serve all the way through World War II in the hands of the Red Army.

https://www.bilibili.com/video/BV1FN41167bq/?vd_source=1b01052b5aca7ea748e1dc18750bb0e8

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