A gun-lock device includes a tubular assembly that fits within the bore and a chamber plug member that fits within the chamber of a firearm. The tubular assembly is partially received into the chamber plug member, wherein spring-loaded expandable arrangement at the end thereof engages with the recess within the chamber plug member to lock the tubular assembly within the barrel. The lock subassembly includes a tumbler cylinder arranged to rotate about the longitudinal axis of the tubular assembly and a set of lock-pins which are disposed parallel to, and in a circular formation about, the longitudinal axis of the tumbler cylinder. The resulting overall arrangement yields a compactly packaged gun-lock device suitable for use in combination with a holster-worn firearm, and the key, with such small size and ornate shape, suitable for being mounted on a ring to be worn by the user at all times. A spring loaded plunger mechanism enhances the speed and ease of operation by adding a self-eject feature to the device.