ammo vs munition

ammo and munition both are nouns.

Word	Noun	Adjective	Verb	Adverb
ammo	Yes	No	No	No
munition	Yes	No	Yes	No

As nouns, munition is a hypernym of ammo; that is, munition is a word with a broader meaning than ammo:

Other hypernyms of ammo include arms, implements of war, weaponry, weapons system.

ammo (noun)	munition (noun)
projectiles to be fired from a gun	weapons considered collectively
	defensive structure consisting of walls or mounds built around a stronghold to strengthen it
	military supplies

ammo (verb)	munition (verb)
	supply with weapons