FRAMES AND RECEIVERS
Under U.S. federal law, the manufacture and possession of firearms for non-commercial purposes (i.e., personal use) has, almost without exception, been unlicensed and legal. Since the 1968 passage of the Gun Control Act, however, anyone intending to manufacture firearms for sale or distribution is required to obtain a Federal Firearms License, and each firearm made intended for sale is required to bear a unique serial number.
Since firearms manufacturers began procuring unfinished frames and rifle receivers from separate, OEM
companies in interstate commerce, specialists, and private individuals
have also purchased and finished these components as "receiver blanks"
at home. Most unfinished receivers from the 20th century could be
finished with hand tools, the common drill press, or machine tools. Certain companies in the 1990s began to sell receiver kits that could include drill bits, stencils, or jigs to aid the finishing process.
It has always been possible to make firearms from raw materials, and more recently it has become popular among firearms hobbyists to produce receivers from plastic with a 3D printer, though the variety of materials and methods used to create these receivers are of greatly varying quality.