.22 vs twenty-two rifle

.22 and twenty-two rifle both are nouns.

Word	Noun	Adjective	Verb	Adverb
.22	Yes	No	No	No
twenty-two rifle	Yes	No	No	No

As nouns, twenty-two rifle is a hyponym of .22; that is, twenty-two rifle is a word with a more specific, narrower meaning than .22:

Other hyponyms of .22 include twenty-two pistol.

.22 (noun)	twenty-two rifle (noun)
a .22 caliber firearm (pistol or rifle)	a .22-caliber rifle