the free bolt stunner is used for emergency, in-the-field euthanasia of large farm-animals that cannot be restrained. it differs from a true captive bolt gun in that the projectile is not retractable; it is similar in operation to a powder-actuated nail gun or conventional firearm. capable of firing only when pressed firmly against a surface (typically the animal's forehead), the device fires a small projectile through the animal's skull. the veterinarian can then either leave the animal to die from the projectile wound or administer lethal drugs.