The term "40" is a commonly used slang in Chicago to describe a handgun that fires .40 caliber ammunition. Unlike "30 poppa," which refers specifically to any compact firearm equipped with a 30-round magazine, "40" identifies the caliber of the weapon rather than its magazine capacity. Despite this distinction, a .40 caliber handgun can also be referred to as a "30 poppa" if it is fitted with an extended 30-round clip, blurring the lines between the two terms in practice.
The use of the term "40" has been heavily popularized through Drill music, where rappers frequently reference firearms as symbols of power, defense, or aggression. Chicago artists, often affiliated with gang culture, have incorporated the term into their lyrics to portray street credibility and survival in a violent environment.
In the song "Don't Know Me" by RondoNumbaNine, he raps, “I’m in traffic with this 40 that got a beam plus a light, you wanna see?”—illustrating not only the caliber but also the added modifications that enhance the weapon’s effectiveness. Similarly, Montana of 300 raps in "Let the 40 Bang," saying, “You see that 30 clip up off that 40 hang,” clearly combining both terms. Here, the firearm is a .40 caliber handgun equipped with a 30-round magazine, making it both a "40" and a "30 poppa" by street definitions.
This interchangeable usage reflects how firearm slang in Drill culture often overlaps, influenced by both the physical characteristics of the weapons and the lyrical need for aggressive imagery.