hired gun vs shooter

hired gun and shooter both are nouns.

Word	Noun	Adjective	Verb	Adverb
hired gun	Yes	No	No	No
shooter	Yes	No	No	No

As nouns, hired gun and shooter are synonyms defined as:

Other synonyms of hired gun include gun, gun for hire, gunman, gunslinger, hit man, hitman, torpedo, triggerman.

hired gun (noun)	shooter (noun)
a professional killer who uses a gun	a large marble used for shooting in the game of marbles
	a person who shoots (usually with respect to their ability to shoot)
	a professional killer who uses a gun
	(sports) a player who drives or kicks a ball at the goal (or a basketball player who shoots at the basket)
	a gambler who throws dice in the game of craps