ammunition vs ammo

ammunition and ammo both are nouns.

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

As nouns, ammunition and ammo are synonyms defined as:

ammunition (noun)	ammo (noun)
projectiles to be fired from a gun	projectiles to be fired from a gun
information that can be used to attack or defend a claim or argument or viewpoint
any nuclear or chemical or biological material that can be used as a weapon of mass destruction