The bolt carrier is a central component of the bolt carrier group (BCG) in firearms like the AR-15, serving as the framework that houses and supports the bolt and facilitates several key functions of the firearm's operation. It works by moving back and forth within the gun's receiver, driven by gas that is redirected from the barrel after each shot. This movement extracts spent cartridges and chambers fresh rounds, effectively resetting the weapon for each subsequent shot. The carrier also plays a crucial role in the firing mechanism: it houses the firing pin and the cam pin, ensuring proper alignment and timing of the firing process. Moreover, its top features a gas key that channels the gas from the barrel to the BCG, ensuring consistent cycling and reliability. Made from high-strength materials like steel or aluminum and often treated with protective coatings, bolt carriers are designed to withstand the pressures and wear of rapid and repeated firing, making them vital for the durability and reliability of the firearm.