The gun in your dream could represent several different things, so please pay attention to the details and to the mood of the dream.
The gun could symbolize the male sex organ, aggression, harshness, and fear.
This dream may have sexual connotations, or your unconscious mind may be telling you not to harbor your negative feelings but express them more freely before they become explosive. On the more positive side of things, the gun could simply represent your need to protect yourself either emotionally or physically or both.
If the gun in the dream is used to hurt or kill you or someone else, please consider your current difficulties, hostile feelings or serious arguments, which you may have within yourself or with others.
See Also: Shooting, Blood