Mishandling a revolver while freeing the cylinder can result in accidental discharge. An accidental discharge can also occur when manually unloading a pistol and when the revolver is equipped with our grips it can also cause an accidental discharge.
The only way that should be able to happen is by pulling the trigger. Most of the newer revolvers have safety's built in to prevent a negligent discharge. By newer I am talking about guns manufactured after 1960 and later.