What gun has the slowest rate of fire?

Fully automatic firearms (machineguns) truly have a rate of fire, as they continue to fire as long as the trigger is held down. Semi-auto, pump, bolt and lever firearms fire one shot, and will either reload, or are reloaded by the shooter manipulating the gun's action. A single shot firearm must be loaded by hand, and would be the slowest of conventional firearms. The absolute slowest rate of fire would be a flintlock rifle, which has a rate of fire by a skilled rifleman of about 2 shots per minute.