To echo what most have said the process is pretty easy. It Pittsburgh you tell the counter that you are declaring a firearm. You check any luggage without a gun in it with them. You fill out a card that goes inside the gun case and then you take then you are directed to the far end of the counters. Past all the other airline ticket counters to where there is a lonely TSA agent whose sole job (to the best of my knowledge) is to give your bag the once over, acknowledge you have that little paperwork, the proper gun case (hard sided and locked) and then they take your bag from you and you continue to the terminal.
Never had a problem with Pittsburgh or most other airports.
There was this time in San Francisco when I told the airline teller I was checking a firearm and she gave me such a disdain of disapproval she basically spat out at me that she didn't want to see it (you're supposed to show them its unloaded and how many bullets you have - depends on the airline) and she tosses me the form and calls security telling them there is a guy with a gun.
Yeah, she was a bitch. But the security guy was solemn and didn't say anything. The TSA agent who went through my bag was very pleasent though. But where in Pittsburgh its a once over, in San Fran she basically unloaded my bag, wiped everything down for explosive residue and then I packed it all back. She told me that the Airline teller was supposed to have verified my firearm and signed off on it but she didn't see the need to send me back so she did it herself.
The whole thing was kind of amusing as she is pulling out my firearm, hatchet, knives, and general survival like gear (did some camping) she didn't comment on any of it and we just chatted away.
So, though most people are giving you the, its not a big deal speech, just be ready in the future if you are ever in a "less than friendly" gun state.
That's before I go on about New York City and Albany New York who have a standing order to arrest anyone who tries to check a firearm while traveling even if its perfectly legal to do so without a NYS Weapons Permit.