Green’s Dictionary of Slang

shotgun n.2

1. (US drugs) a type of pipe used for smoking marijuana.

[US](con. 1970) J.M. Del Vecchio 13th Valley (1983) 120: The shotgun was a tube of seven Coca-Cola cans taped together end-to-end. Grass [...] was burned in the second can. The shotgunner blew into a large opening in the first can and the smoke [...] cooled in the five following tins until it peed out of a tiny puncture at the end of the tube [....] where the shotgunnee could stand back eight or ten inches, mouth gaping, and swallow the smoke stream.
[US] ‘Stoner Dict.’ on Lil’ Bastard’s House of Heaven 🌐 Shotgun – Thing on my bong.

2. (drugs) a means of intensifying the effect of cannabis smoke: the cigarette is reversed, the lit end in the mouth, sealed there by the lips; its holder then blows into the cigarette and the resultant powerful stream of smoke passes into a receiver’s mouth.

personal recollection.
[US]E.E. Landy Underground Dict. (1972).
[US]Eble Campus Sl. Mar. 5: shotgun [...] That shotgun took my head off.
[US](con. 1969–70) D. Bodey F.N.G. (1988) 273: Callmeblack winks at me. ‘Hey, little brother, how about one more shotgun?’.
[US]Bentley & Corbett Prison Sl. 72: Shotgun A powerful and explosive way to smoke a marijuana cigarette. This is accomplished by lighting a joint [...] then placing the lit end inside your mouth ensuring the fire does not hit your tongue or the inside of your mouth. You then place your lips around the joint in an air-tight fashion, position the other end several inches in front of a person’s face and blow forcefully. This will produce a powerful stream of smoke which comes out the other end [...] (Archaic: bang a reefer).
[US](con. 1970s) G. Pelecanos King Suckerman (1998) 170: ‘I’m tellin’ you, man, I don’t want no shotgun.’ Karras put the lit end of the joint in his mouth. He blew on the joint, sent a concentrated jet of smoke into the room.
Online Sl. Dict. 🌐 shotgun n [...] 2. a method of smoking marijuana whereby one person inhales from the source and then blows the smoke into someone else’s mouth. They inhale it and the chain continues. Apparently, the term can also apply to cigarette smoking.
[US]Da Smokehouse Marijuana Gloss. 🌐 shotgun – same as a ‘shottie’. shotgun [s-london] – carbing the bong. shottie – taking the joint and reversing it and blowing the smoke into another person’s mouth.
[US]G. Pelecanos Right As Rain 204: The four of them stood [...] and smoked the joint. Strange took Quinn’s shotgun, but Juana refused it.
[US]D. Sedaris When You Are Engulfed in Flames (2009) 245: ‘A shotgun? What’s that?’ [...] ‘You lie back while I blow smoke into your mouth’.