Go online for the TSA rules for checking a firearm and ammunition in checked baggage as well the rules of the airline you are flying with. Additionally, the destination you are to arrive at has to be considered as well.
The XD case should be fine. Any ammo you bring has to be in the original container. I have a Pelican pistol case I put several things into when I travel: Guns, mags, ammo for each, knives, multi tool. All fit, though it is a little snug.
You must tell the counter person (At baggage check counter) that you want to check a firearm. They will give you a short form ( A card really) to fill out, ask you a question or two and then tell you to put the card in the bag with the case. Then you will be escorted to the TSA scanner bank where a nice TSA person may ask you about the lock you have on the box, whether you have the key, or perhaps another question. They'll tell you to stand by while they send it through the XRay and if everything is copacetic, they'll give you a thumbs up.
This is how it works at Tampa intl and Shuttlesworth Intl (Birmingham, Alabama {Roll Tide!}) Airports.
On the XD, My daughter liked my 40 Sub compact so much, I bought her a 9mm! The .40 was just a little too snappy for her but the 9mm is perfect!
I hope you enjoy your vacation!
Here's the TSA rules :
Firearms and Ammunition | Transportation Security Administration