canister shot vs ammo

canister shot and ammo both are nouns.

Word	Noun	Adjective	Verb	Adverb
canister shot	Yes	No	No	No
ammo	Yes	No	No	No

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

canister shot: a metallic cylinder packed with shot and used as ammunition in a firearm
ammo: projectiles to be fired from a gun

Other hypernyms of canister shot include ammunition.

canister shot (noun)	ammo (noun)
a metallic cylinder packed with shot and used as ammunition in a firearm	projectiles to be fired from a gun