If you ask ten shooters to name the most popular caliber in the world, you'll probably hear a few different answers. The honest answer depends on how you define "popular." But if you're looking for one cartridge that has earned its place as a global standard, the answer is clear: the 9mm Luger, also known as 9x19mm Parabellum. In this guide, we'll break down why the 9mm is considered the most popular caliber in the world, how it stacks up against other leading cartridges like the .22 LR and the …