Swiss Mini Gun
The SwissMiniGun has a total length of 5.5 cm and is 2.34 millimetres in caliber. This firearm is a scaled-down model of the Colt Python. It's a keychain with a bang.
I once saw a gun like this in a museum in St. Augustine. It was described as a "lady's gun" and that it was designed to deliver a fatal blow by being shot down the ear canal.