Common bullet weights for 9mm include 115gr, 124gr, 125gr, and 147gr. Generally speaking, heavier bullets hit harder, have more recoil, and are more expensive. Most people practice with 115gr ammo, and carry heavier stuff for personal defense.

Thanks to the lower energy of the bullet it's much less deadly. However - and this is important - it's still deadly enough. A 9mm round in the chest can easily perforate your lungs, cut a major artery or destroy your heart.

The popularity of the 9mm can largely be attributed to law enforcement agencies and the military. The average consumer often takes their cues from these organizations, and the 9mm is the caliber of choice for most police stations and the FBI.

Caliber: In Firearms, the diameter of the bore measured from land to land, usually expressed in hundredths of an inch (. 22 cal) or in millimeters (9mm). In ammunition, a naming system that indicates cartridge dimensions as well as bore diameters, and can be the same as the Firearm caliber.