From the ATF website -

Transferring/Shipping/Possession of Firearms:

4. May I lawfully transfer a firearm to an individual who resides in a different State? What if the individual resides within the same State?

Under Federal law, an unlicensed individual is prohibited from transferring a firearm to an individual who does not reside in the State where the transferee resides. Generally, for a person to lawfully transfer a firearm to an unlicensed person who resides out of State, the firearm must be shipped to a Federal Firearms Licensee (FFL) within the recipient’s State of residence. He or she may then receive the firearm from the FFL upon completion of an ATF Form 4473 and a NICS background check. More information can be obtained on the ATF website at www.atf.gov and http://www.atf.gov/firearms/faq/unlicensed-persons.html. The GCA provides an exception from this prohibition for temporary loans or rentals of firearms for lawful sporting purposes. For example, a friend visiting you may borrow a firearm from you to go hunting. Another exception is provided for transfers of firearms to nonresidents to carry out a lawful bequest or acquisition by intestate succession. This exception would authorize the transfer of a firearm to a nonresident who inherits a firearm under a will or by State law upon death of the owner. See 18 U.S.C. § 922(a)(5)(A).

In regard to transferring firearms between individuals residing in the same state, any person may sell a firearm to an unlicensed resident of the State where he resides as long as he or she does not know or have reasonable cause to believe the person is prohibited from receiving or possessing firearms under Federal law. Please note that there may be State and local laws that regulate firearm transactions. Any person considering acquiring or transferring a firearm should contact his or her State Attorney General’s Office to inquire about the laws and possible State or local firearms restrictions. A list of State Attorney General contact numbers may be found at http://www.naag.org/.