You must declare all firearms to the airline during the ticket counter check-in process.
The firearm must be unloaded.
The firearm must be in a hard-sided container.
The container must be locked. A locked container is defined as one that completely secures the firearm from access by anyone other than you. Cases that can be pulled open with little effort do not meet this criterion. The pictures provided here illustrate the difference between a properly packaged and an improperly packaged firearm.
We recommend that you provide the key or combination to the security officer if he or she needs to open the container. You should remain present during screening to take the key back after the container is cleared. If you are not present and the security officer must open the container, we or the airline will make a reasonable attempt to contact you. If we can't contact you, the container will not be placed on the plane. Federal regulations prohibit unlocked gun cases (or cases with broken locks) on aircraft.
You must securely pack any ammunition in fiber (such as cardboard), wood or metal boxes or other packaging that is specifically designed to carry small amounts of ammunition.
You can't use firearm magazines/clips for packing ammunition unless they completely and securely enclose the ammunition (e.g., by securely covering the exposed portions of the magazine or by securely placing the magazine in a pouch, holder, holster or lanyard).
You may carry the ammunition in the same hard-sided case as the firearm, as long as you pack it as described above.
You can't bring black powder or percussion caps used with black-powder type firearms in either your carry-on or checked baggage.
TSA: Traveling with Special Items