This element is borrowed straight from the dance halls of Jamaica, where DJs reveled in the cacophonous din of street life years before DJ Whoo Kid teamed up with 50 Cent. While actual gunshots remain a signal of terror, gunshot sound effects signal something entirely different. In the context of a mixtape they do not indicate impending doom but rather sonic momentum.
As contemporary rap embraces cheap computer-generated production values (much like the Jamaican dancehall culture that preceded it) the gunshot drops have become more pervasive and essential. As much as they may reflect an urban reality, their primary function is as an indicator of the newfound urgency of rap's low-budget auditory onslaught.