automatic rifle vs machine rifle

automatic rifle and machine rifle both are nouns.

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

As nouns, automatic rifle and machine rifle are synonyms defined as:

automatic rifle and machine rifle: self-loading rifle capable of automatic fire

Other synonyms of automatic rifle include automatic.

automatic rifle (noun)	machine rifle (noun)
self-loading rifle capable of automatic fire	self-loading rifle capable of automatic fire