MOMENTOUS DISCOVERIES often come about by accident. James Goodyear left rubber on a hot stove overnight and invented vulcanization. Louis Pasteur tried to kill some chickens with cholera bacteria and vaccinated them instead. I tried to turn my son's 870 Express Jr. into a slug gun for him and wound up making a great turkey gun for myself. The gun formerly known as "John's" is short, light, handy, and deadly.