horse pistol vs shooting iron

horse pistol and shooting iron both are nouns.

Word	Noun	Adjective	Verb	Adverb
horse pistol	Yes	No	No	No
shooting iron	Yes	No	No	No

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

horse pistol: a large pistol (usually in a holster) formerly carried by horsemen
shooting iron: a firearm that is held and fired with one hand

Other hypernyms of horse pistol include handgun, pistol, side arm.

horse pistol (noun)	shooting iron (noun)
a large pistol (usually in a holster) formerly carried by horsemen	a firearm that is held and fired with one hand