It isn't illegal to build your own firearms as long as it doesn't violate any NFA rules which include fully automatic weapons, "sawed off" shotguns, short-barreled rifles (SBR), and weapons with bores greater than 0.5" (.50 cal). If you sell a firearm you build/manufacture then you are breaking the law unless you have an FFL Type 07 manufacturing license. In other words you can build/manufacture all the weapons you want as long as you keep them for yourself and don't violate the NFA rules.
It isn't illegal to build your own firearms as long as it doesn't violate any NFA rules which include fully automatic weapons, "sawed off" shotguns, short-barreled rifles (SBR), and weapons with bores greater than 0.5" (.50 cal). If you sell a firearm you build/manufacture then you are breaking the law unless you have an FFL Type 07 manufacturing license. In other words you can build/manufacture all the weapons you want as long as you keep them for yourself and don't violate the NFA rules.
NFA "rules" ... SHALL NOT BE INFRINGED MOFO's