"This publication is designed to help you comply with Federal and State firearms laws. Specifically, it will assist you in complying with the Gun Control Act of 1968 (GCA). The GCA prohibits licensees from selling or delivering a firearm to a nonlicensee whose receipt or possession of the firearm would violate State or local laws applicable at the place of sale or delivery. In addition, this book will assist you in making lawful over-the-counter sales of rifles and shotguns to out-of-State residents--transactions that must meet the legal requirements of both your State of residence and the purchaser's State of residence. State Laws and Published Ordinances -- Firearms also includes a 'Ready Reference Table' to provide you with additional assistance for your business operations. When deciding whether to make a sale, you should first consult the full text of the State requirements, and if appropriate, contact State and local authorities before making a decision."
ATF Publication 5300.5
U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, Publications: http://www.atf.gov/publications/