The hellfire revolver is a crude firearm that fires rounds that collapse on impact, sending a violent burst of raditation into the target. This not only causes a lot of damage, but also increases the risk that the target will suffer from radiation sicness or cancer. These are plot elements, though.
Hellfire revolvers are highly illegal, as they cause excessive harm and pollute the environment. It costs an item schtick to own a hellfire revolver.
Against targets resistant to radiation, the damage of the HellfireRevolver is reduced by three points.