18 U.S.C. 922(a)(3) & (5), 922(b)(3), 27 CFR 478.29 & 478.30
"A person may only acquire a firearm within the person’s own State, except that he or she may purchase or otherwise acquire a rifle or shotgun, in person, at a licensee’s premises in any State, provided the sale complies with State laws applicable in the State of sale and the State where the purchaser resides. A person may borrow or rent a firearm in any State for temporary use for lawful sporting purposes."

and


18 U.S.C. 922(a)(3) and 922(b)(3)
"A person not licensed under the GCA* and not prohibited from acquiring firearms may purchase a firearm from an out-of-State source and obtain the firearm if an arrangement is made with a licensed dealer in the purchaser’s State of residence for the purchaser to obtain the firearm from the dealer."


*Gun Control Act of 1968