zip gun vs shooting iron

zip gun and shooting iron both are nouns.

Word	Noun	Adjective	Verb	Adverb
zip gun	Yes	No	No	No
shooting iron	Yes	No	No	No

As nouns, shooting iron is a hypernym of zip gun; that is, shooting iron is a word with a broader meaning than zip gun:

Other hypernyms of zip gun include handgun, pistol, side arm.

zip gun (noun)	shooting iron (noun)
a crude homemade pistol	a firearm that is held and fired with one hand