side arm vs shooting iron

side arm and shooting iron both are nouns.

Word	Noun	Adjective	Verb	Adverb
side arm	Yes	No	No	No
shooting iron	Yes	No	No	No

As nouns, side arm and shooting iron are synonyms defined as:

side arm and shooting iron: a firearm that is held and fired with one hand

Other synonyms of side arm include handgun, pistol.

side arm (noun)	shooting iron (noun)
a firearm that is held and fired with one hand	a firearm that is held and fired with one hand