artilleryman vs machine gunner

artilleryman and machine gunner both are nouns.

Word	Noun	Adjective	Verb	Adverb
artilleryman	Yes	No	No	No
machine gunner	Yes	No	No	No

As nouns, artilleryman and machine gunner are synonyms defined as:

Other synonyms of artilleryman include cannoneer, gunner.

artilleryman (noun)	machine gunner (noun)
a serviceman in the artillery	a serviceman in the artillery