Mike Williams finds out why armies use one type of bullet, while gangsters use another and what the phrase full-metal jacket tells us about our qualms about killing each other. The bullet has been at the heart of the world's battles for many centuries. Although the essential idea hasn't changed much since the 15th Century, the way the bullet and its use has evolved is revealing. He hears from doctors, soldiers and criminals about why such a small object causes so much damage and what it means to shoot someone, and be shot.