Doorgunner. I travel a good bit on US Airways with a shotgun to shoot across the country. You have to declare the arm and show it is unloaded and no ammo at the airport and sign a decleration. You have to do this inside the airport, not at the curb, so leave yourself alot more time(i almost missed my flight several times). I have never traveled with anything but my shotgun, and an AR looks alot more formidable to the uneducated, so you may get some additional questions, I would call the airlines first also. People behind you in line, as well as the airline employees, sometimes give me a strange look with a shotgun, also, I have run into airline employees whom I have had to explain the process to(evidently they don't do it much) which takes a little more time. If you are going to be in the Pittsburgh area, check out the following website for Greater Pittsburgh Gun Club, there may be a shoot that interests you, and they have a 400 meter rifle range to shoot on.
http://www.greaterpghgunclb.com/