Why is the 9mm handgun so popular in gangster movies?

9X19mm is the most common handgun caliber in the world. It's easy to use and cheap. Handguns in the caliber usually have high capacities. The most often portrayed "nine" is a Glock 17 or 19, because of their generic appearance. The slightly more powerful.40 caliber (10X21mm) is slowly taking it's place and has been mentioned in rap music.