automatic weapon vs automatic gun

automatic weapon and automatic gun both are nouns.

Word	Noun	Adjective	Verb	Adverb
automatic weapon	Yes	No	No	No
automatic gun	Yes	No	No	No

As nouns, automatic weapon and automatic gun are synonyms defined as:

automatic weapon and automatic gun: a firearm that reloads itself and keeps firing until the trigger is released

Other synonyms of automatic weapon include automatic firearm.

automatic weapon (noun)	automatic gun (noun)
a firearm that reloads itself and keeps firing until the trigger is released	a firearm that reloads itself and keeps firing until the trigger is released