How is the gun that Atticus shot the dog with symbolic?

There is the obvious symbol of guns as an extension of manhood, but in this case Atticus does kill a dog that is potentially harmful to the community. Tom is also killed with rifles by the guards, but he is clearly not harmful to the community. Atticus also says later that he doesn't want Jem to think a hero is a man standing in the street with a gun. So the gun embodies a thematic element for the book as a whole.