My experiences
fivepaknh: When I fly to pickup fugitives for extradition purposes, I carry my sidearm on my person. Otherwise, I just declare the unloaded handgun in my checked luggage at the ticket counter.
The FARs (FAA regs) state lockable, hard-side case. I usually use a hinged, foam-lined, polypropylene pistol case inside my hard-side suitcase. Some airlines want their agent to view the UNLOADED handgun--others just tell me to sign the 'firearms unloaded' tag and place it in the inner case (and some just say in the suitcase). Sometimes I run a white cable-tie thru the barrel and/or magazine well to further demo that it is unloaded.
If you get the third degree, ask the agent to page the Ground Security Supervisor for clarification. Other than the pilot, this guy has final say as to who flies with what.
LUCK!!