Abstract: The present invention presents a locking assembly which may be installed in a firearm during manufacture or as a retrofit to an existing firearm and which locks the bolt of the firearm against normal movement in the receiver. The assembly includes a cylinder lock installed in the stock of the firearm below the receiver and which has a locking element which is extendable through an aperture in the receiver to engage a blind aperture provided in the bolt. In this manner the assembly locks the bolt in a position which prevents loading and firing of the weapon and which also prevents its disassembly until the lock is released. The locking assembly may also be provided in kit form for retrofitting particular makes and models of firearms wherein the kit includes the lock assembly, a replacement receiver, a replacement bolt and a template for locating the position on the stock in which to install the lock assembly.