A factory or aftermarket conversion allows the Glock 23, originally chambered in .40 S&W, to fire 9mm Luger cartridges. This involves replacing the .40 caliber barrel with a 9mm barrel, often opting for a threaded variant to accommodate suppressors or other muzzle devices. This modification provides a cost-effective way to own a pistol capable of firing both calibers, especially for those already owning a Glock 23 frame. This conversion necessitates a compatible magazine designed for 9mm rounds.
The ability to change calibers offers versatility and potential cost savings on ammunition, particularly given the generally lower price of 9mm ammunition compared to .40 S&W. A threaded barrel extends this versatility further by allowing for the attachment of accessories like suppressors for reduced noise and muzzle flash, or compensators for recoil mitigation. This adaptability makes the platform attractive for various applications, from target shooting and home defense to professional use. The practice of modifying Glock pistols has a long history within the firearms community, driven by the desire for customization and specific performance characteristics.