[1] Any transfer of possession of a gun from a resident of one state to a resident of another state must, under federal law, be done by an FFL. The FFL in effecting the transfer must comply with all requirements of federal law, i. e., (1) the transferee must be present and present proper identification; (2) the transferee must meet the federal minimum age requirement to receive possession of a gun from an FFL (18 for long guns and 21 for handguns); (3) the FFL must get a completed form 4473 from the transferee; and (4) the FFL must perform the necessary background check to establish that the transferee is not a prohibited person. In addition, the FFL transfer must comply with any applicable state laws (e. g., waiting periods, registration, etc.).
[2] In the case of a handgun, the FFL must be in, and the transfer must take place in, the transferee's state of residence.
[3] In the case of a long gun, if the transferee is present in the FFL's place of business in a state other than the transferee's state of residence, the FFL may transfer the long gun to the transferee if (1) the long gun would be legal to possess in the transferee's state of residence; and (2) the transfer complies with the laws of the state in which it's taking place and the state in which the transferee resides. But some FFLs don't want to get involved in those transactions.
[4] In general it would be legal for a resident of one state to ship a handgun (or long gun, for that matter) to an FFL in another state for the purpose of effecting the transfer of that gun to a resident of that state. BUT some FFLs will not accept delivery of a gun from an individual but only from another FFL. That is the FFL's choice. An FFL may also charge a fee for his participation in the transaction. It's a good idea to work out the details and charges ahead of time and in writing. If an FFL will accept a gun for transfer from an individual, he will usually require a copy of the transferor's driver's license.
