The gun in the dream has something to do with the assertiveness of the dreaming and generally with aggressively asserted power.
The weapon can give self-protection and self-assertion. To what extent other people are affected by this, the dreamer must examine closely. In Freud is it a male sexual symbol, also signs of sexual tension (the gun is well known tense).
For example, aiming at someone in the dream without firing suggests a failure in love or in another area of life.