The handguns must be unloaded and in a locked case in your check in luggage. Only you can have a key to the case.
Ammunition must be in boxes designed to carry ammunition (the original factory box is fine).
You must declare to the ticket agent at the ticket counter that you have unloaded firearms in your luggage. I was able to get both handguns and a box of ammunition for each in the case.
Mac’s Guide to Flying with a Firearm, is an excellent source of information. Be sure to download the information on flying with a firearm from both the TSA web site and the website of the airline you are flying on. The TSA web site provides more general guidelines and your airline’s web site will have specifics on what that particular airline requires.