My brother flew from Houston to Philly with his reproduction Enfield (US Civil War) rifle. He had to buy a full-size gun case and take the stock off the barrel to get the thing to fit (even in Texas, people clear a path if you come into an airport with a full-size gun case). The woman who inspected it--which included peeking down the barrel to see if it was loaded--was immensely relieved to see that it was disassembled.

He could not, however, check his can of black powder and had to buy a new one at Gettysburg.