Imagine a gun as small as a quarter palm of your hand. The Swiss Minigun is the world’s smallest gun. A revolver by manufacture, it is a double-action. 09 caliber six-shooter that’s just over two inches (5.5 cm) long weighing 0.7 oz. (19.8 g). The SwissMiniGun is as tiny as a key but is capable of firing tiny bullets at over 270mph.