BAR vs machine rifle

BAR and machine rifle both are nouns.

Word	Noun	Adjective	Verb	Adverb
BAR	Yes	No	No	No
machine rifle	Yes	No	No	No

As nouns, machine rifle is a hypernym of BAR; that is, machine rifle is a word with a broader meaning than BAR:

BAR: a portable .30 caliber automatic rifle operated by gas pressure and fed by cartridges from a magazine; used by United States troops in World War I and in World War II and in the Korean War
machine rifle: self-loading rifle capable of automatic fire

Other hypernyms of BAR include automatic, automatic rifle.

BAR (noun)	machine rifle (noun)
a portable .30 caliber automatic rifle operated by gas pressure and fed by cartridges from a magazine; used by United States troops in World War I and in World War II and in the Korean War	self-loading rifle capable of automatic fire