The experience of the War of 1812 led the War Department to issue a request for contract proposals for firearms with interchangeable parts. Previously, parts from each firearm had to be carefully custom fitted; almost all infantry regiments necessarily included an artificer or armorer who could perform this intricate gunsmithing. The requirement for interchangeable parts forced the development of modern metal-working machine tools, including milling machines, grinders, shapers and planers. The Federal Armories perfected the use of machine tools by developing fixtures to correctly position the parts being machined and jigs to guide the cutting tools over the proper path. Systems of blocks and gauges were also developed to check the accuracy and precision of the machined parts. Developing the manufacturing techniques for making interchangeable parts by the Federal Armories took over two decades; however, the first interchangeable small arms parts were not made to a high degree of precision. It wasn't until the mid-century or later that parts for U.S. rifles could be considered truly interchangeable with a degree of precision. In 1853, when the British Parliamentary Committee on Small Arms questioned gun maker Samuel Colt, and machine tool makers James Nasmyth and Joseph Whitworth, there was still some question about what constituted interchangeability and whether it could be achieved at a reasonable cost.
