It is unlawful to discharge within the city limits any pistol, revolver, rifle or shotgun which may be used for the explosion of cartridges, or any gas operated gun or any device for propelling missiles, or any slingshot or missile propelling device, or any bow made for the purpose of throwing or projecting missiles of any kind by any means whatsoever, whether any instrument is called by any name set forth above or by any other name; provided, that this section has no application in cases involving the discharge of a firearm for lawful purposes. (Prior code § 7-1-14 (b))