Well, that's not what we were discussing. And it is not against the law to make your own cartridge firearms, either, for personal use. If you intend to go into business, then you must acquire the proper licensing. Since 1986, is has been illegal to make machineguns for personal use. You may still make short barreled shotguns/rifles, pen guns (Any Other Weapon, in BATF speak), and suppressors, AFTER the proper form has been approved by the BATF and the proper tax paid ($200 for SBS/SBR and suppressors, $5 for AOW). Prior to the GCA of '86, a non-felon over the age of 21 could legally make their own machinegun by filling out the same form and paying the $200 tax. These taxes were created in the GCA of 1928, prior to that, there were no limitations.