Green’s Dictionary of Slang

(US) a homemade firearm capable of firing single bullets;also as v. (see cite 1957).

1949		‘Hal Ellson’ Duke viii: Zip – a gun made from a toy ‘Airplane Gun’ that shoots a .22 bullet.
1953		W. Brown Monkey On My Back (1954) 118: Pepe himself had a zip-gun – a toy pistol which he had [...] rigged up with tape and heavy rubber bands in such a way that it would fire a .22 bullet. [Ibid.] 240: Remember, too, that Pepe took a pot shot at a prowl car even if it was with a zip.
1957		D. Burley N.Y. Amsterdam News 24 Aug. 13: Bands of zip-gunning teen-agers.
1959		‘Paul Merchant’ ‘Sex Gang’ in Pulling a Train’ (2012) [ebook] The knife would be useless against the zip, held so professionally in the hands of the girl [ibid.] The firing pin of the zip gun ready to drive the .32 slug through the car radio antenna barrel.
1964		P. Marshall ‘Some Get Wasted’ in Clarke Harlem, USA (1971) 350: The cat had gone to church packing his zip that morning and gone down to lock with the Crusaders that afternoon.
1965		C. Brown Manchild in the Promised Land (1969) 16: I had shot him in the leg with a zip gun.
1975		E. Torres Carlito’s Way 7: Then the zip guns came out, metal tubes with door latches as firing pins set off by rubber bands.
1989		A. Vachss Hard Candy (1990) 42: Half-ass zip guns that would blow up in your hand when you pulled the trigger.
1992		Bentley & Corbett Prison Sl. 89: Zip also Z A homemade firearm. A zip is generally made of a short length of pipe, usually about four to ten inches long, with an inside diameter the same size as the circumference of the bullet to be fired. The bullet is placed in one end of the pipe while a pointed steel rod is placed in the other end. The pointed end of the rod is used to detonate the bullet and is activated by a sharp blow using the heel of one’s hand or a small, solid object.
1995		(con. 1985–90) P. Bourjois In Search of Respect 60: Maybe some zip guns [then]. Now it’s Uzis.
2023		Rayman & Blau Riker’s 184: Yeah, .22-caliber bullets will fit inside an antenna. We can get the rubber band. We can get the hospital tape. You got a scrub brush, and the antenna goes into the groove of the brush. [...] Take some cardboard and take the nail and bend it like a hook and put the rubber band and boom, it hits the back and the bullet comes out.