machine rifle vs automatic rifle

machine rifle and automatic rifle both are nouns.

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

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

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

Other synonyms of machine rifle include automatic.

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