A blow gun includes a hollow ammunition chamber having an internal volume that is large enough to hold at least 30 spherical projectiles, for example plastic BBs. The ammunition chamber has a breath receiving orifice, and a firing port. A barrel obtrudes from the hollow ammunition chamber through the firing port. The barrel has a cylindrical bore therethrough, that defines an internal diameter that is greater than the spherical projectile diameter but no greater than 1.7 times the spherical projectile diameter. The barrel has an outer surface that is in sliding contact with the firing port. The barrel may have a storage position in which most of the barrel is disposed within the internal volume of the hollow ammunition chamber, and a firing position in which most of the barrel is disposed outside of the hollow ammunition chamber.