The Gun Control Act of 1968 (GCA) permits an unlicensed individual to make a firearm for personal use, but not for sale or distribution. However, the law does not explicitly preclude an unlicensed person from later selling, giving away, or otherwise transferring a homemade firearm to another person as long as it was originally intended for personal use. A gun explicitly made for personal use can be sold or transferred in the same way that a factory-made firearm of that same class can be sold or transferred.
The key in determining whether a homemade gun can be legally sold or transferred rests with knowing the intent of the maker when the gun was first created. Relevant factors in determining the transferor's intent may include: the length of time between the creation of the firearm and its transfer; the specific reason for the sale or transfer; and whether the maker of the firearm frequently sells or transfers homemade firearms. For example, a time lapse between creation and sale of many years, a reason for sale that has no sinister overtones, and a transfer that is one-in-a-lifetime for the transferor, would indicate an original intent to keep the gun. By contrast, quickly transferring a gun right after its creation, to someone who could not legally possess a firearm, by someone who regularly transfers such guns, would indicate a lack of intent to keep the gun.
If a homemade firearm is sold or transferred (as long as the gun was originally made for personal use), the sale is subject to the same set of transactional regulations that govern sales between private individuals. For example, while federally licensed firearms dealers are required to conduct background checks on prospective purchasers and maintain records of all firearms transactions, the sale of a firearm between two private individuals is not subject to the same level of scrutiny.
According to the Bureau of Alcohol, Tobacco and Firearms (BATF), an individual can sell or transfer a firearm to another person without record keeping as long as both individuals reside in the same state and the recipient is not someone who falls within the categories of prohibited persons (such as a convicted felon). There may be state or local regulations that otherwise impact the transaction, but as far as federal law is concerned, it is not necessary for the seller to be licensed, nor is the seller required to perform a background check of the buyer. There is no federal regulation that precludes a transaction involving a homemade firearm from being sold or transferred in a similar manner, as long as such a sale or transfer was not the original intent of the firearm's maker.
Federal law does not require a homemade gun to have an identifying marker (such as a serial number), as long as it remains in the possession of the original maker. However, if the gun is subsequently sold or otherwise transferred, it should be marked prior to its disposition. The ATF suggests that all homemade firearms be marked with a serial number as a safeguard in the event the firearm is lost or stolen, but requires it if the gun is otherwise lawfully transferred in the future.
A homemade firearm may also be transferred to another person via a "gun trust." A gun trust is a trust created in order to enable a gun owner to legally transfer firearms while exempting the trust's beneficiaries from background checks, fingerprinting, and law enforcement approval. Typically, gun trusts are used to transfer a class of weapons that are regulated by the National Firearms Act (NFA) and Title II of the GCA and subject to a high level of scrutiny, including machine guns, silencers, short-barreled rifles, and short-barreled shotguns. (For a comprehensive explanation of gun trusts, please see Nolo's article, Using a Gun Trust to Pass on Firearms.)
It is important to note, however, that before these types of NFA-regulated weapons can even be created, an individual must submit a tax payment and seek approval from the BATF (a machine gun, for example, cannot be made unless it is for a federal or state agency). Consequently, it is unlikely that most lawful homemade guns will be in the class of firearms typically found in gun trusts.