Buying a firearm outside your home state is legal in some combinations and a federal felony in others. The difference comes down to two questions: what kind of firearm, and who is handing it to you. Here is what federal law actually permits, in the order a counter clerk would ask.
Federal law cares about where you actually live, not where you are standing. 18 U.S.C. 922(b)(3) bars a licensed dealer from selling or delivering a firearm to anyone the dealer knows or has reason to believe resides in another state, with one narrow exception. A dealer also may not sell where the buyer's purchase or possession would violate state law or a published local ordinance at the point of delivery.
No federal provision lets a nonresident walk into an out-of-state shop and leave with a handgun. The lawful route is a transfer, not a sale: the dealer ships the handgun to a licensed dealer in your home state, and you take possession there after meeting the 27 CFR 478.99 requirements, including Form 4473 and a background check. You can buy the gun in another state. You cannot receive it there.
The rifle and shotgun exception is real but narrow. 27 CFR 478.96(c) lets a licensed dealer sell or deliver a rifle or shotgun to a nonresident only if the buyer meets the dealer in person at the licensed premises, the dealer complies with the background check rules, the buyer completes Form 4473, and the sale, delivery and receipt fully comply with the law in both states.
Two details trip people up. First, nothing in the current text requires the two states to share a border, so the old neighboring-state assumption no longer describes the law. Second, the exception covers rifles and shotguns only. A stripped frame or receiver is neither at the point of sale, so it follows the handgun rule and has to go through a dealer in your home state.
Two private parties in different states cannot simply hand off a firearm. Under the same statute a person may not receive a firearm obtained outside their state of residence, and may not transfer one to a resident of another state. The workaround is the standard one: ship it to a dealer in the buyer's state and let that dealer run the transfer. The recognized exceptions are a bequest or inheritance, and a temporary loan or rental for lawful sporting purposes, which is why borrowing a rifle for an out-of-state hunt differs from buying one.
Moving to a new state with your own firearms is lawful. An unlicensed person may ship a firearm interstate to themselves or to a licensee, must declare it to the carrier, and cannot use the mail for a handgun, because pistols and revolvers are nonmailable to private parties under federal postal law. Long guns can travel by common carrier. What you cannot do is ship a firearm to a private party in another state and call it a gift.
Plan for the second half of the transaction before you pay for the first. A receiving dealer will want the sender's information, a copy of the selling dealer's license when one is involved, and will run Form 4473 and a background check as with any in-state purchase. Your state may add a waiting period, a purchase permit, a magazine limit or an approved handgun roster, and those requirements attach to the transfer even when the sale happened somewhere with looser rules. The waiting period and paperwork checklist is worth reading before you commit. Ask about the transfer fee up front, and confirm the shop accepts private-seller transfers.
Buying a long gun out of state without checking whether your home state would have allowed you to buy it there is the most common error. The two-state test is not a formality; it is the condition that makes the sale lawful at all. The second is treating a gun show badge as a loophole. A dealer at a show is still bound by the state their license sits in, so the same limits travel to the table.
Suppressors and short-barreled rifles add a layer that general transfer rules do not fully answer, because state law now carries most of the weight. If that is your purchase, start with how states split on SBR and suppressor law and the dealer-side walkthrough in No Form 4 Does Not Mean No Rules, then get the receiving dealer's position in writing. And if you need a receiving dealer at all, find an FFL dealer in your state before you buy, not after.
None of this is legal advice, and state rules move faster than federal ones. The statute and the regulations linked above are the floor, not the ceiling.