Why do you think the narration switches focus to the gun after the characters leave the ruined city?

The ending of the story allows the events to remain open-ended. The crew leaves the planet hoping to come back, believing that the gun has been destroyed. Only the reader knows that a small army of self-repairing gadgets and an atomic warhead are moving toward the gun. Dramatic irony occurs when the reader has more knowledge about a particular outcome than the characters. So, in "The Gun," the reader knows that the gun will repair itself, but the characters flying away are unaware of this information. This ending evokes a mood of fear and suspense as the reader realizes that the weapon of destruction will regenerate itself and will most likely strike the crew and others once they return to the planet. (plato)

Investigation on the gun or To investigate on the gun.