six-gun vs six-shooter

six-gun and six-shooter both are nouns.

Word	Noun	Adjective	Verb	Adverb
six-gun	Yes	No	No	No
six-shooter	Yes	No	No	No

As nouns, six-gun and six-shooter are synonyms defined as:

six-gun and six-shooter: a pistol with a revolving cylinder (usually having six chambers for bullets)

Other synonyms of six-gun include revolver.

six-gun (noun)	six-shooter (noun)
a pistol with a revolving cylinder (usually having six chambers for bullets)	a pistol with a revolving cylinder (usually having six chambers for bullets)