In the story Dave demonstrates that he is just a 17 year old "boy" and not ready to make the rite of passage into manhood.  He felt that a gun was a status symbol to be a man and if he owned it everyone would respect him.  This was a total fallacy and only made the other people in his life ridicule him and laugh at him.  He then decided to escape reality (punishment and restitution) by getting on the train with the gun and hoping he will end up in a town where people will respect him.  Since he is using the gun as a trophy for manhood this will only lead me to believe he is headed for bigger issues and problems in life.  By leaving, the law could be after him since he broke the law and he could have made his family situation worse because they will have to pick up where he left off and make restitution for his wrongs.  He definitely made a series of bad decisions.