A firearm barrel lock for preventing the accidental or unauthorized discharge of a firearm is provided. The barrel lock includes a dummy cartridge that is adapted to be received by a cartridge chamber of a firearm, a shaft that is insertable down the bore of the firearm and includes a first end that is engagable the dummy cartridge, and a lock that is releasable secured to a second end of the shaft which extends beyond the end of the barrel which precludes the removal of the shaft from the barrel.