There is one firearm which actually fits in the game. It is not very accurate and needs to be fired at a closed range, it fires only one pellet, and since it takes forever to reload, after fired, it can be used as a club: the hand cannon.
http://www.uh.edu/admin/engines/earlyhandcannon.jpg
What you see underneath is not a trigger, it is a metal spike, which they'd use as a handle to fire, then use the spike to bludgeon heads