Green’s Dictionary of Slang

twenty-two n.

[abbr.; note thirty-eight n. (1)]

(US) a .22 calibre pistol.

[US]D. Hammett ‘Night Shots’ in Nightmare Town (2001) 81: A twenty-two and my forty-four — which I keep in the car — are the only pistols in the place.
[US]R. Chandler ‘Finger Man’ in Pearls Are a Nuisance (1964) 108: I got my twenty-two, which is all the gun I have, and hid in the bushes.
[US]N. Algren Never Come Morning (1988) 149: Which of your guests filed the numbers off that twenty-two?
[US]H. Rap Brown Die Nigger Die! 20: Even a lot of these so-called ‘militants’ go around pulling their 22’s on Black people and ‘tomming’ when the white man comes around.
[US]S. King Dead Zone (1980) 283: I gave him the .22.
[US]C. Stroud Close Pursuit (1988) 244: We’re trying to lift a latent off a twenty-two.
[US]E. Richards Cocaine True 78: The guy pulled a .22 from the side of the car.
[US]C. Cook Robbers (2001) 224: Only he carried a thirtytwo, not a twentytwo.
[UK]L. Theroux Call of the Weird (2006) 192: They would send a goon squad to [...] finish him off ‘execution-style with a dirty twenty-two.’.