Green’s Dictionary of Slang

1. a small-calibre weapon, e.g. a .22; thus used derog. for any unimpressive gun.

[1789		J. O’Keeffe Highland Reel 66: For a gun, pip, pop, change my little pop-gun].
1831		Satirist (London) 7 Aug. 143/3: [in fig. sense] [A]fter a fortnight’s drill, the learned gentleman used to fire off his pop-guns in the House of Commons.
1844		Polynesian (Honolulu, HI) 21 Dec. 1/1: St Sebastian Sockdolager, Esq., the editor of the ‘National Pop-gun’.
1849		E.E. Napier Excursions in Southern Africa II 389: I instantly stepped into the next room, to get the old pop-gun there; [...] my finger was in an instant on the trigger .
1860		N.E. Police Gaz. (Boston, MA) 18 Aug, n.p.: What kind of a hand does Pop Gun Pressy hold — winning or losing.
1869		Man about Town 20 Nov. 87/1: ‘What do you think of No. 8 and the “popgun” now, you simple Simon?’.
1877		E.L. Wheeler Deadwood Dick in Beadle’s Half Dime Library I:14/1: P’arps ye kin tell me who fired the popgun, a minnit ago, w’at basted my ole pard.
1888		Kipling ‘The Likes O’ Us’ in Civil & Military Gaz. 4 Feb. (1909) 104: ‘Stick to your bloomin’ pop-guns [...] an’ don’t talk to a better man than you’.
1897		O. Wister Lin McLean 158: He and his pop-gun will be guttin’ some blameless man.
1907		D. Stewart Vultures of the City in Illus. Police News 12 Jan. 12/3: ‘Put that pop-gun away’.
1920		T. Dreiser letter 23 Sept. in Riggio Dreiser-Mencken Letters II (1986) 396: He is as a pop-gun to a howitzer.
1928		A.W. Upfield House of Cain 263: You just drop your little pop-gun tood sweet, or I’ll drop you.
1940		Ed Leffingwell ‘Little Joe’ [comic strip] Ten of ’em right behind us, chief, and us without even a popgun.
1947		R.S. Spears ‘A 22-Gun Ranger Walks’ Texas Rangers Jan. 🌐 ‘An’ he’s packin’ a twenty-two, one-shot gun, too!’ The little pop gun was passed around.
1984		P. Corris ‘Heroin Annie’ in Heroin Annie [e-book] You, put the popgun over there near the telly and then go back near the door.
1985		(con. 1968) D.A. Dye Citadel (1989) 41: Grunt on the other side of the window from me fondled his M-16 [...] You’d think the safety of the entire company depended on one stupid fucking grunt and his lousy space-age plastic popgun.
2012		(con. 1943) G.S. Manson Coorparoo Blues [ebook] ‘What’s this fucken popgun?’ It was a short.22 pistol.

2. thus attrib. use of sense 1, in fig. use, small, insignificant.

1853		W. Sketch & ‘Nelse’ The Down-Trodden 18/1: Little pop-gun newspaper editors demanded the execution of the laws.
1918		R.H. Knyvett ‘Over There’ with the Australians 189: Official reports of the later battles in 1918 tell us that the shell-fire on the Somme was a mere popgun show to these battles.
2013		T. Piccirilli Last Whisper in the Dark 262: He [...] wore a popgun .22 on his belt.