I have flown a lot with weapons, and the process has always been easy. Gun goes in a hard, lockable gun case. At the airport I go to the check in counter, the person at the desk has me open the gun case (I dont lock it yet) and they check to make sure the guns are not loaded and sign a slip and put it inside the gun case. Then I bring the gun case to the oversized items area. The TSA person checks the guns again and then has me put 3 locks on the gun case. They take the gun case, load it on a conveyer belt and Im off to the terminal.
Very simple process, but it varies depending on the airport. I've never had a problem with the process though.