A firearm for implementing an improved 9 mm cartridge is provided, wherein the improved 9 mm cartridge includes a 9 mm bullet associated with a 45-9 cartridge casing, wherein the 9 mm bullet weights at least 90 grains and wherein the 45-9 cartridge casing is configured to contain a propellant sufficient to propel the 9 mm bullet to a velocity of at least 1600 feet per second. The firearm may include a barrel, wherein the barrel is configured to operably interact with the 9 mm bullet and a chamber, wherein the chamber includes at least one chamber portion sized and shaped to operably associate with the 45-9 cartridge casing and a free-bore, wherein the free-bore includes at least one free-bore portion sized and shaped to operably associate with the 9 mm bullet.