First comes the bullet, the submachine gun fires a pistol bullet. Various calibers of pistol bullets had emerged on Earth, but one of them not only had a strong vitality of over a century but also became the standard caliber for most submachine guns. The one Li Lin chose was this kind of bullet - 9mm Parabellum pistol bullet.
Despite a slight deficiency in stopping action, this type of pistol bullet survived from the early 20th century to the 21st century. Larger or more powerful calibers like the Magnum series, .45 ACP, 7.62mm Tokarev never achieved that status. Completing the research and development of this type of pistol bullet earlier would certainly assist in the future selection of submachine guns.
There are a fair number of pistols that fire 9mm Parabellum bullets, but 9mm Mauser won the selection for its unique traits.
Magazine capacity, accuracy, rate of fire, and technical conditions are precisely the keys to its standout status.
