I've been to a castle close by where I live, where they have this room called "rustkammaren" (I have no idea how to translate that). It's basically a room full of medieval weapons. They have hand-crossbows in there! Like, tiny crossbows with a pistol grip! I imagine it would be possible to dual-wield those. I have no idea how you load them though.
They also had this massive musket.. with nine barrels! It looked amazing! It is said that the only guy who ever fired it was killed by the recoil (it has only been fired once..). Unfortunately you're not allowed to take pictures in there, but if you ever come to Stockholm/Uppsala, Sweden, make sure you visit Skokloster Castle.