I have done this dozens of times, not a big deal at all.
Gun needs to be in a hard lockable case. Go to the ticket counter, tell the person there that you need to declare a firearm, they will ask you to demonstrate that its not loaded. They will make you sign a declaration form that will go into the case. They will then send the gun in the unlocked case to TSA for further inspection and TSA will inspect the firearm, lock the case and send it on its way.
At your destination grab gun case off the baggage carousel. Sometimes its held with oversize items or at the airlines baggage office in baggage claim.
I suggest a gun case with wheels as you may have quite a hike to get from baggage to your transportation.
I bought my first AR from Jims in BR and flew into Reagan National Airport right outside of Washington DC with it when I lived in Northern Virginia.
This post was edited on 7/31 at 6:39 pm