WASHINGTON — When a decades-old law banning undetectable firearms expires less than a month from now, federal agents say a plastic weapon created on a 3-D printer could emerge as a national security threat. The homemade plastic gun, known as the "Liberator .380" and made with a computer blueprint, a 3-D printer and plastic resin, could pass through security checkpoints without setting off metal detectors. The gun uses only the smallest bits of metal for ammunition... (GunPolicy.org)