The information I got when I asked the question on another forum:
I travel with firearms all the time...and airsoft quite a bit. You do not need TSA locks for a firearm and it's actually discouraged. If TSA wants to inspect a bag designated as a firearm they will contact the passenger for the combination. Use combination locks not keys you will inevitably misplace a key. Have a couple of spare locks in the box for when they are damaged in transit...you can't get your bag back on the airplane for the trip home without locks and finding locks as you rush to the airport is a pain in the a$$.
Don't buy a $12 gun box and expect it to pass inspection. If it's too flexible and can be significantly separated even with the locks on; they will reject your firearm for transport. It needs to be pretty rigid...ask around and see if you can borrow a Pelican box or something for transport.
It is a very straight forward process at the airport. Shooting equipment is accepted as checked baggage. All your other gear INCLUDING BBs should also go as checked baggage. Your bayonet in checked bag, no problem, your BBs, no problem, DO NOT bring stuff like fake grenades and mines these are a problem. Fake grenades I won't travel with at all, they are a pretty big grey area that I don't want to have to be the Supreme Court test case on. Don't plan on bringing anything airsofty in carry on baggage...when you are tired or late you will make a mistake and end up with some 'splaining to do.
The airline you are flying has firearms requirements listed on their websites. Don't bother telling them its airsoft, just declare it as a firearm and do the process...its easier than explaining what airsoft is with 1000 people eyeing the apparent "guns" your transporting. You can have the batteries in the case, I just recommend that they aren't in the gun...it looks funny on xray and they are more likely to want to dig around in there. The "process" entails you opening the box to show the lady at the counter that its a firearm telling her it is unloaded and mostly likely telling her that she needs to give you one of the day glow orange tags behind the counter to fill out since she may or may not know. Then you put the tag in the box, lock it up and tell her you'll stand around until TSA clears your bag, if you don't have to bring it to TSA yourself of course...this also depends on the airport. DO NOT let them tell you the firearms tag goes on the outside of the bag, it does not, it goes on the inside.
BBs show up as metal due to the barium in them...put these on top of any luggage you have them in so that TSA doesn't have to dig through everything to find them. Over-pack your BBs in a zip-lock bag so that if/when the crappy bag they came in bursts at the seams you don't have BBs all over the inside of your luggage. Do not transport your magazines with BBs in them...especially drum magazines...guess what they look like on xray!
Have your name, address and phone number on the inside the case as well as on the outside of the case so there can be no question who they should need a contact for a stray bag. Lastly, I very much recommend putting a piece of duct tape on your bag(s) and in big sharpie put the destination airport code on there. Yes, the bag tag has it too but it can be torn off. Doing that has gotten sensitive equipment to the right airport for me on more than one occasion; after that its just a matter of going to the airline office at your arrival airport and saying where's my "lost" bag. This is much easier if it's not at DCA when you are in SFO.
Your gun box will sometimes though not always show up at the special bag pick up, not the carousel. It really depends on the airport.
So to sum up when checking a firearm, you must:
Declare to the representative that you are checking a firearm (If a Security Checkpoint is prior to the ticket counter, you must declare the existence of a firearm to security personnel.)
Present firearm(s) unloaded and sign a "Firearms Unloaded" declaration. Basically just a little Orange tag that goes INSIDE the box. Do not let them tell you it has to go on the outside, it does not.
Lock the firearm(s) in a hard-sided, crush-proof container.