Green’s Dictionary of Slang

(drugs) any makeshift instrument used to inject when one does not have a syringe.

1933		D. Maurer ‘Junker Lingo’ in AS VIII:2 27: If the addict cannot obtain the regulation needle he may construct an emergency gun from a medicine dropper and safety pin.
1949		Monteleone Criminal Sl. (rev. edn).
1953		Anslinger & Tompkins Traffic In Narcotics 308: emergency gun. A hypodermic needle made from a medicine dropper and a safety pin.
1959		J.E. Schmidt Narcotics Lingo and Lore.
2001		ONDCP Street Terms 8: Emergency gun — Instrument used to inject other than a syringe.