Hey DP, having flown around the world with airguns for comps, I will tell you that you need to have your rifle in a hard plastic case that has the holes for pad locks to go through. Your gun will be inside when you take it to the ticket counter for the airlines. The ill informed person behind the counter will ask whats in the case and you tell them its a Firearm, I dont say AIRGUN unless someone asks how its operated. I tell them its a Pellet gun if they ask. Per policy its supposed to be void of air when flying. At that point all airlines will have you fill out a red or orange 3x5 inch card with your signature on it, and the ticket person will have you open your case, look inside quickly and throw the 3x5 card inside. Then you lock the case with the padlocks that ONLY YOU have a key for. You do not have a TSA approved lock. What sense does that make to have a lock on your case that the TSA has a key for, and can open up your case and take what they want. You then hang in the ticket are 15 minutes in case TSA wants to look inside for whatever reason. If the ticket person doesnt yell for you after 15 mins you proceed onto the security gate and hope your gun makes it ok. This is the process around the world, with same exceptions in places like Colombia, Spain and England, where the Police fill out some paperwork also.
PS....if the gun has an air gauge it should show 0, or close to....only in Colombia, did the Policia National ask me to unnscrew a bottle off a gun.