Figured it was odd we didn't have a thread for oddities, abominations and obscure firearms, so let's start one.
The Porter Turret Rifle was a rather bizarre attempt to circumvent Samuel Colt's revolver patent, using a "cylinder" with the pivot perpendicular to the barrel. This monstrosity is a percussion rifle and the chambers are in that circular section, facing in all directions (including one pointed directly at the shooter).
As well as being a terrible idea on principle, it was prone to row ignition; not so great when your rifle is designed to have a chamber pointed straight at you, and supposedly one of its designers was killed while demonstrating it.