An AR-9 barrel fits AR-15 style pistol-caliber carbines chambered in 9mm Luger. It delivers reliable performance and accuracy for AR-9 builds. Lengths typically range from 4 to 16 inches. The barrel pairs with AR-15 upper receivers and blowback bolt carrier groups. It works with 9mm magazines and dedicated 9mm lowers. Builders also use magwell adapters and compatible handguards. Shooters choose it for home defense, competition, and recreational shooting.