Firearms do not have to be inside checked baggage. I have flown with firearms several times lately and in most airports you check your bags at the counter and then take your guns to the TSA for inspection. Once inspected you are not allowed to handle the gun case again. When you arrive at your destination each airport is different, at some, guns come in with other baggage, at others they come in to a separate counter.
TSA web site https://www.tsa.gov/travel/transporting-firearms-and-ammunition