You can’t do curbside check-in, so prepare yourself to go inside to your airline counter. When checking in, calmly tell the ticketing agent, you have a firearm to declare. It helps if you don’t yell something like “I’VE GOT A GUN!!!” Unless you live in one of the Republik states, the agent won’t even bat an eye. They deal with this all the time. The agent will tell you what do to and when.