Long guns can be purchased at any FFL, on location, by walk-in customers regardless of their state of residence. (The legality of taking it home with you is entirely your own concern, depending on your local home state laws.)
In other words, I can drive to Texas from Idaho, buy a rifle or shotgun, and drive home with it.
It used to be that out-of-staters could only buy a long gun in a neighboring state. So a Nevada FFL could sell a long gun, over the counter, to residents of Nevada, Arizona, Utah, California, Oregon, and Idaho.
This is no longer the case, and over-the-counter sales of long guns can be made regardless of one's state of residence.