air rifle vs air gun

air rifle and air gun both are nouns.

Word	Noun	Adjective	Verb	Adverb
air rifle	Yes	No	No	No
air gun	Yes	No	No	No

As nouns, air rifle and air gun are synonyms defined as:

air rifle and air gun: a gun that propels a projectile by compressed air

Other synonyms of air rifle include airgun.

air rifle (noun)	air gun (noun)
a gun that propels a projectile by compressed air	a gun that propels a projectile by compressed air