Attested in "True Grit" by Charles Portis, 1968, but most likely much older.

The derivation is probably from the percussion "cap," a small metal cylinder open at one end with an amount of shock-sensitive explosive, usually fulminate of mercury, used to set off the powder charge in a muzzle-loading firearm.

The modern derivation, however, is probably from the "cap gun," a toy firearm using paper "caps" containing Armstrong's mixture or a similar substance to provide the small explosions.
"I have never busted a cap (bust a cap) on a woman or anybody much under sixteen years but I will do what I have to do." -- "Lucky" Ned Pepper
by ET Molligee September 21, 2014
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A slang phrase referring to the posession and use to a certain individial of a firearm or any other object resembling a firearm that emits any sort of a projectile.
"Imma bust a cap in yo mothafuckin ass bitch!"
by www.blingblingx.da.ru December 1, 2004
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To discharge a handgun, usually a 9mm, in the direction of an enemy or a rival gang.
Im gonna bust a cap in his punk ass
by HeavenlyHost July 4, 2003
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1.Man that "fiddy sent" busted a cap in his ass.
2.I busted a cap in "Fiddy sents" asss
by ub3r n00b3r September 24, 2004
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To discharge a round of ammunition from a firearm, usually a handgun.
Fuck wit me, and I'll bust a cap in yo ass biatch!!!!
That fool was disrespectin' a brutha so I had to straight bust a cap in his ass!
by Streetsouljah September 6, 2006
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To unload your gun on someone and ultimatley, kill them. A very popular activity in the ghetto.
Nigga 1: Hey you want some of dis sheeit?
Nigga 2: Ah, I don wan dat shit.
Nigga 1: I don give a fuck, I don't play that shit, and I'm about to bust a cap motha nigga.
by jakrel August 13, 2005
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Peeing after you cum pushing the left over cum out of your penis.
I just jerked off then I was busting a cap in the toliet.
by Cellucci November 30, 2018
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