I have an individual from Alaska who wants to purchase a rifle through my FFL here in Montana while visiting. The ATF is ok with this but based on their response below they shift the "burden of proof" onto the FFL holder (licensee). Montana state law doesn't seem to have an opinion one way or another re selling rifles to out of state residents so it's considered to be legal here. An FFL in MT can refer to the NICS participation map and sell a rifle/shotgun to residents of green or blue states without breaking federal or state laws. What isn't clear to me is whether or not other states have laws preventing over-the-counter sale of rifles to residents of other states.
https://www.fbi.gov/file-repository/nics-participation-map.pdf/view
https://www.atf.gov/qa-category/conduct-business#out-of-state-resident
May a licensee sell a firearm to a nonlicensee who is a resident of another State?
Generally, a firearm may not lawfully be sold by a licensee to a nonlicensee who resides in a State other than the State in which the seller’s licensed premises is located. However, the sale may be made if the firearm is shipped to a licensee whose business is in the purchaser’s State of residence and the purchaser takes delivery of the firearm from the licensee in his or her State of residence. In addition, a licensee may sell a rifle or shotgun to a person who is not a resident of the State where the licensee’s business premises is located in an over–the–counter transaction, provided the transaction complies with State law in the State where the licensee is located and in the State where the purchaser resides.
[18 U.S.C. 922(b)(3); 27 CFR 478.99(a)]
https://www.fbi.gov/file-repository/nics-participation-map.pdf/view
https://www.atf.gov/qa-category/conduct-business#out-of-state-resident
May a licensee sell a firearm to a nonlicensee who is a resident of another State?
Generally, a firearm may not lawfully be sold by a licensee to a nonlicensee who resides in a State other than the State in which the seller’s licensed premises is located. However, the sale may be made if the firearm is shipped to a licensee whose business is in the purchaser’s State of residence and the purchaser takes delivery of the firearm from the licensee in his or her State of residence. In addition, a licensee may sell a rifle or shotgun to a person who is not a resident of the State where the licensee’s business premises is located in an over–the–counter transaction, provided the transaction complies with State law in the State where the licensee is located and in the State where the purchaser resides.
[18 U.S.C. 922(b)(3); 27 CFR 478.99(a)]