TSA cutting locks on cases with declared firearms
Correct about the need for TSA licks on the outer luggage and private locks on the firearm case whether inside of luggage or on its own.
Know the rules and don't give TSA any reason to give your case special attention. I use to get my firearm case opened most of the time and then a TSA agent informed me that if they can not see on X-ray the firearm is unloaded they will have you open the case to verify it is. He suggested disassemble or open the action to show it is mot loaded and ready to fire.
Now when I fly I swing out the cylinder in a revolver or remove the slide on a semi and have never been asked to open my case since. This is not required but makes the TSA job easier and less reason to mess with my case.