What determines a gun's purpose? The maker's intent (or some sort of combined intent of the persons who make the gun)? Is the purpose of a gun unique to each gun, or do all guns have the same purpose(s) by virtue of being categorized as "guns"? Is the reason guns were first made necessarily the reason guns are made now?

I say there is no inherent purpose for guns. Of course, guns can be used for many things, including killing, injuring, recreation, sport, getting food (hunting), robbing (intimidation), collecting (admiration of firearms), and many more. Guns have many uses, but no particular purpose.