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Before we get into our recommendations, let’s do a general overview of how a BCG works within an AR-15. Understanding the bolt carrier group parts and how they interact is important to diagnose any issues and ensure your gun has proper reliability and feeding.

A BCG works with the gas system to cycle, fire and eject rounds as you fire. More specifically, the bolt carrier group will load a new round into your chamber, extract the spent casing, and repeat the process all over again.

Below are some of the key pieces you’ll find within a complete bolt carrier group and the general role they play in the process:

• Firing pin – After the trigger is pulled, the hammer rotates forward, hitting the firing pin. The firing pin will then strike the primer of the chambered round and the gun will fire.
• Carrier / gas key – Your gas key sits on the top of the BCG and connects to the gas tube. When a round is fired through your barrel, gas is funneled back through the gas key and forced down into the body of your bolt carrier group.
• Bolt carrier – The bolt carrier is the body of your BCG. The high-velocity gas will fill the chamber and force your BCG rearward, compressing the buffer and buffer spring. To handle the high temperatures and pressure levels, you’ll find bolt carriers and bolts are made from very high quality ordinance steel.
• Bolt – The bolt assembly features locking lugs that rotate to lock and unlock the bolt inside the chamber. As the bolt carrier drives backward, the cam pin rotates the bolt, unlocking it from the chamber and allowing the complete BCG to move rearward.
• Bolt gas rings – These three rings sit on the back of the bolt to create a seal between the bolt and the bolt carrier, trapping gas expansion inside the BCG.
• Extractor – The extractor hooks onto the rim of your round, pulling it out of the chamber.