Air Gun, an instrument for the projection of bullets by means of condensed air, generally either in the form of an ordinary gun or of a stout walking-stick, and about the same length. A quantity of air being compressed into the air chamber by means of a condensing syringe, the bullet is put in its place in front of this chamber and is propelled by the expansive force of the compressed air, which is liberated on pressing the trigger. The simplest form of air gun is the popgun, made by fitting a wooden piston to the hollow shaft of a goose quill. See AIR; AIR COMPRESSOR; COMPRESSED AIR.