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AR-15 Parts In addition to the upper and lower receivers, the AR-15 is composed of a number of other parts, including the: Barrel: The barrel is the part of the AR-15 that fires the bullet. It is available in a variety of lengths and calibers. Bolt carrier group: The bolt carrier group is the part of the AR-15 that chambers the round, fires the bullet, and extracts the spent cartridge. Charging handle: The charging handle is the part of the AR-15 that is used to load the rifle and cycle the bolt carrier group. Handguard: The handguard is the part of the AR-15 that protects the shooter's hand from the heat of the barrel. Buttstock: The buttstock is the part of the AR-15 that the shooter shoulders when firing the rifle. Pistol grip: The pistol grip is the part of the AR-15 that the shooter grips with their hand when firing the rifle. Trigger: The trigger is the part of the AR-15 that fires the bullet. Magazine release: The magazine release is the part of the AR-15 that allows the shooter to remove the magazine from the rifle. Safety selector: The safety selector is the part of the AR-15 that allows the shooter to switch between safe, fire, and semi-automatic modes. Buffer tube: The buffer tube is the part of the AR-15 that contains the buffer and spring. The buffer and spring help to absorb the recoil of the rifle when it is fired.