My experience is exactly the same as Waynes, no problems. When you walk up to the ticket counter, say the words "Ma'am/Sir, I'll need a declaration form when you get a second"... he/she will know what you mean. Don't say "I've got a gun in here" or any other stupidity like that. Checking a firearm through the airlines is a simple task if the person on the other side of the counter knows their job, and they usually do. I've travelled 30-40 times with checked firearms and NOT ONE SINGLE TIME has an counter agent ever wanted to actually see the gun or verify themselves that it was unloaded. They simply hand me the form, watch me lock the case, and take my bag from me and throw it on the conveyor. It's dead simple.
A must watch video: http://www.youtube.com/watch?v=mGjddG5Owsc
The TSA has the right to search your bags. They may need to do this after the bag goes through the scanner and disappears from your sight down the conveyer belt at check-in. Bags are randomly checked at various points in the custody chain once you hand it to them at the counter. If your bag gets selected or there is a "hit" on your bag by a dog or scanner, they WILL open it. You can use any kind of lock you want on the outside of your luggage...
but if it's not a TSA lock, they'll cut it.
HOWEVER, YOU CANNOT USE TSA LOCKS ON YOUR FIREARMS CASES. This is Federal Law. The owner of the guns/case is the only person who shall have access to the contents. I use regular Masterlock brass stuff currently, and put a lock on every hole each of my cases has.
For smaller firearms cases that are going inside your checked luggage, you put your regular locks on your firearms case, and then you can use a TSA lock on the luggage itself... that way they have access to the luggage, but not the firearms case inside.
Under no circumstances should you give your KEY or COMBO to your regular locks to any TSA employee. TSA personnel are not allowed to open you firearms cases, nor handle any firearm. If your checked baggage gets tagged for a search, and the TSA people for whatever reason feel they must search your firearms case too, they will contact you (hopefully via your cel phone) and bring you to a secure area to open it for them. I HIGHLY SUGGEST YOU REQUEST THE PRESENCE OF A LEO when you open the case. They should have no problem accommodating you. It is almost a certainty that the person who needs you to open the case is simply following a protocol, but has zero clue about guns. They won't have any idea what they're looking at once you open the case, so have a LEO there so there is no misunderstanding. I would also insist that the opening of the case be done while under video surveillance.
This is another good reason to ensure your gun cases have your contact information on them, even if it's just your initials and a phone number. I have seen flights delayed because of baggage issues and individual passengers called off the plane while still at the gate who never got back on, and can totally see a "firearm case issue" resulting in you missing your flight. The quicker they can contact you, the better.
WATCH THE VIDEO!!! It'll change the way you travel.