There will, later, be an option to load ammunition of the appropriate type into a weapon, much in the same way as storing one item in another (such as a backpack). The lack of a Hand option on most of them is probably an oversight, and until they are loaded they will need to be either stored, or held in a free hand.
Until the rules are finalised and released for that feature, it's hard to be precise, or sure about exactly how it will work.
"May the Grace of Ara go with you, and His Vengeance be wrought upon your enemies."
Thanks. I'm mostly asking because I'm working on some custom images for them and trying to get an idea how they're supposed to look. I guess I'll just come up with something I'd find reasonable and cross my fingers.