assault rifle vs assault gun

assault rifle and assault gun both are nouns.

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

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

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

assault rifle (noun)	assault gun (noun)
any of the automatic rifles or semiautomatic rifles with large magazines designed for military use	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