No need to contact Delta beforehand sir..
You will need to declare your weapons at the check-in counter. The ticket agent will have you open your case, show that the weapons are unloaded, and then require you to sign a form affirming the weapons are unloaded. Then, depending on the airport, you will be directed to TSA or wait for TSA to come to you to inspect the weapons and case. You will need to remain there until the inspection is complete and re-lock your own case before they send it on it's way. This could take 5 minutes or an hour depending on the airport. Give yourself plenty of time just in case.
Upon re-entry to the USA, you will need to claim your guns at the US Customs office in the airport of your first point of entry into the USA. Then you will re-check your weapons domestically as you did for your initial departure.
