Gun show loophole - link is to Wikipedia
Since there's no federally mandated background checks at gun shows for residents of the same state, that might work. Typically only applies to states in the South and West and away from the coasts, sadly. Long guns and shot guns look to be easier to get than handguns in a several jurisdictions. And, obviously, you have to live in the same state where the show is.
I'm sure there's exceptions both ways, but it basically looks like every state that voted for Trump has this loophole, and none of the ones that went for Biden do.
FWIW, I live in a state with very restrictive rules and I've toyed with moving to a nearby state with lax ones. I don't have an involuntary hold as an adult, but I just figured it would be easier to get a gun that way. Move a hundred miles, get a new driver's license, register your car and register to vote in the new jurisdiction. Not sure what other ID they ask for beyond that, that I still need to research.