A magazine lock for a firearm includes a magazine well and a magazine latch. The lock includes a tube nut positioned within a housing. The tube nut is connected to the magazine latch of the firearm. When tightened down, the tube nut prevents the magazine latch from releasing a magazine from the magazine well. A tool is provided to engage the tube nut and rotate the tube nut within the housing permitting the magazine latch to release the magazine. The housing includes a biased engagement feature that selectively prevents the rotation of the tube nut within the housing. The tool is configured to overcome the biased engagement feature and to engage the tube nut so that rotation of the tool rotates the tube nut. A breech block inserted into the top of a magazine inserted into the firearm may also be used to lock the firearm.