No, perfectly legal to sell across state lines, to a licensed dealer, including pawn shops and gunsmiths.
Some old guns are worth more in parts than whole!
Not legal to sell across state lines to a private party.
Unless the the gun is a pre-1898 antique.
As I said, across statelines you must use an FFL.
No matter what state you reside in.
If it’s pre 1898 you can sell in to any one in the US and personally ship it via USPS legally (Not sure about HI or AK)