assault gun vs assault rifle

assault gun and assault rifle both are nouns.

Word	Noun	Adjective	Verb	Adverb
assault gun	Yes	No	No	No
assault rifle	Yes	No	No	No

As nouns, assault gun and assault rifle are synonyms defined as:

assault gun and assault rifle: any of the automatic rifles or semiautomatic rifles with large magazines designed for military use

assault gun (noun)	assault rifle (noun)
an armored vehicle with the chassis of a tank (but no turret) and a large gun; used as an antitank weapon and to support infantry	any of the automatic rifles or semiautomatic rifles with large magazines designed for military use
any of the automatic rifles or semiautomatic rifles with large magazines designed for military use