the bolt consists of a heavy rod made of corrosion-resistant alloys, such as stainless steel. it is held in position inside the barrel of the stunner by means of rubber washers. the bolt is usually not visible in a stunner in good condition. the bolt is actuated by a trigger pull and is propelled forward by compressed air, a spring mechanism, or by the discharge of a blank round ignited by a firing pin. after striking a shallow but forceful blow on the forehead of the animal, spring tension causes the bolt to recoil back into the barrel.