Semi-automatic firearms, including the AR-15 lower receivers, are generally legal to manufacture for private individuals under federal law. However, some states/municipalities restrict either the manufacture of certain firearms, or, more recently, the personal manufacture of a firearm with a 3D printer and/or CNC machine. GG makes no claim regarding your local manufacturing legalities. In some localities, lower receiver files provided by Ghost Gunner may require special licensing to manufacture and/or possess.
Under federal law, manufacturing firearms for purpose of sale and distribution without an FFL is prohibited. Without an FFL, you should manufacture firearms for personal use only. Recent ATF determinations have signaled that allowing others use of your CNC equipment may itself constitute manufacturing, therefore Ghost Gunner advises GG owners to neither print firearms for other individuals, nor allow other individuals to use their Ghost Gunner to manufacture firearms without the advice of counsel.