Abstract: A universal gun lock for insertion into barrel of a gun. The gun lock has a shaft assembly which is inserted into the muzzle end of a bore of the barrel. The lock assembly is held on the external end and the internal end extends into the chamber. An expandable locking cup is expanded by retracting an inner shaft. The locking cup moves outwardly far enough so that it abuts the shoulder of the chamber and cannot be pulled out. A center shaft is extended causing the locking cup to ride down a ramp and contract so that it may be pulled out of the barrel. Preferably, the lock assembly and an inner and outer shaft are provided with a selection of locking ramps and expandable locking cups so that a gun dealer needs only have one lock and shaft assembly with various locking ramps and expandable cups for different sizes of guns. The present invention also includes the process of using the universal lock.