9mm

The 9mm Luger cartridge combines a flat trajectory with moderate recoil. It establishes a statistically backed reputation as a highly effective cartridge. The FBI released a detailed report of the positive combat effectiveness of the 9mm cartridge compared to the .45 and the .40 Caliber cartridges. The report showed that the new powders and advanced bullet designs in modern 9mm defensive loads allowed for the caliber to deliver similar performance to bigger calibers such as the .45 and the .40. So on top of that having less recoil, less wear, cheaper ammo, and higher capacity the 9x19mm has become the preferred cartridge for self defense.