Gunsmith Part 16: Diagnosing and Repairing Common AR-15 Bolt Carrier Group Failures
The AR-15 platform is renowned for its modularity, reliability, and widespread adoption. At the heart of its operation lies the bolt carrier group (BCG), a critical assembly responsible for chambering, firing, and extracting cartridges. Its crucial and proper function is essential. In our ongoing Gunsmith series, we’ve explored various aspects of AR-15 maintenance, customization, and repair. This installment, Gunsmith Part Sixteen, delves into diagnosing and repairing common AR-15 bolt carrier group failures. From identifying potential issues to implementing effective solutions, we’ll equip you with the knowledge and skills to keep your AR-15 running smoothly and reliably.
In previous installments, we’ve discussed topics ranging from barrel selection and gas system tuning to trigger upgrades and optic mounting. We’ve laid a foundation for understanding the AR-15’s inner workings, preparing you for more advanced maintenance and troubleshooting. This episode builds upon that knowledge, focusing specifically on the vital bolt carrier group. This guide will allow you to expand your knowledge and gain valuable insights into resolving malfunctions and extending the lifespan of your AR-15 rifle.
This article will explore common BCG failure points and provide step-by-step instructions for diagnosing malfunctions and implementing necessary repairs. We will cover the essential components of the BCG, common failure modes, how to inspect them, and repair or replace broken parts.
Understanding the AR-15 Bolt Carrier Group
The AR-15 BCG is a complex assembly consisting of several key components, each playing a vital role in the rifle’s operation. These components include the bolt, bolt carrier, gas key, firing pin, cam pin, and firing pin retaining pin. Understanding the function of each component is essential for effective diagnosis and repair.
The Bolt
The bolt locks into the barrel extension, securing the cartridge for firing. It houses the extractor, which removes spent casings, and the ejector, which expels them from the rifle.
The Bolt Carrier
The bolt carrier houses the bolt and provides the mass necessary for reliable cycling. It interacts with the gas system to cycle the action.
The Gas Key
The gas key directs gas from the gas tube into the bolt carrier, driving the bolt rearward and initiating the cycling process.
The Firing Pin
The firing pin strikes the primer of the cartridge, igniting the gunpowder and initiating the firing sequence.
The Cam Pin
The cam pin rotates the bolt, locking and unlocking it from the barrel extension.
Firing Pin Retaining Pin
This simple pin prevents the firing pin from moving forward unless the bolt is fully locked.
A properly functioning bolt carrier group is essential for reliable AR-15 operation. When a failure occurs, it can manifest in various ways, including failure to feed, failure to extract, failure to eject, and light strikes. Understanding the underlying causes of these failures is crucial for effective troubleshooting.
Common AR-15 Bolt Carrier Group Problems and Solutions
Several common issues can plague the AR-15 bolt carrier group, leading to malfunctions and unreliable performance. By understanding these common failure points, you can proactively inspect your BCG and address potential issues before they escalate.
Failure to Extract
This is the failure of the extractor to grab onto the case rim and pull it out of the chamber.
Problem: A dirty or damaged extractor is a frequent culprit. Carbon buildup, worn extractor springs, or chipped extractor claws can prevent proper engagement with the cartridge rim.
Solution: Thoroughly clean the extractor and extractor channel using a solvent and a brush. Inspect the extractor for any signs of damage, such as chips or cracks. Replace the extractor spring if it appears weak or worn. In some cases, replacing the entire extractor may be necessary. A enhanced extractor spring can help to improve extraction.
Failure to Eject
This malfunction occurs when the spent casing is extracted from the chamber but not forcefully ejected from the rifle.
Problem: A worn or broken ejector is a common cause. The ejector is a small, spring-loaded pin located in the bolt face. It forcefully ejects the spent casing from the rifle after extraction.
Solution: Inspect the ejector for any signs of damage or wear. Ensure the ejector spring is functioning correctly. Replace the ejector and/or ejector spring if necessary. Make sure to use the correct punch when removing and installing the ejector retaining pin.
Light Strikes
This happens when the firing pin strikes the primer of the cartridge, but not with enough force to ignite the gunpowder.
Problem: A dirty or damaged firing pin can cause light strikes. Carbon buildup or a bent firing pin can impede its ability to properly ignite the primer.
Solution: Clean the firing pin and firing pin channel thoroughly. Inspect the firing pin for any signs of damage, such as bending or breakage. Replace the firing pin if necessary. Check the firing pin protrusion to ensure it meets specifications.
Gas Key Issues
The gas key directs gas from the gas tube into the bolt carrier. It can often become loose over time or even damaged.
Problem: Loose gas key screws, gas leaks, or a damaged gas key can disrupt the cycling of the action. This results in failures to cycle properly or at all.
Solution: Inspect the gas key screws to ensure they are properly torqued and staked. If necessary, remove the screws, clean the threads, apply a thread-locking compound, and re-torque the screws to the manufacturer’s specification. Staking the screws prevents them from loosening under recoil. Consider replacing the gas key if it’s damaged or heavily eroded.
Cam Pin Wear
Problem: Excessive wear on the cam pin can cause cycling issues and potentially damage the upper receiver.
Solution: Regularly inspect the cam pin for wear. Replace the cam pin if it shows signs of excessive wear or deformation. Ensure proper lubrication of the cam pin and bolt carrier interface.
Diagnosing Bolt Carrier Group Problems: A Step-by-Step Guide
Effective diagnosis is the first step towards resolving any AR-15 bolt carrier group problem. A systematic approach can help you quickly identify the root cause of the issue.
Visual Inspection
Begin by visually inspecting the entire BCG assembly. Look for any signs of damage, such as cracks, chips, or excessive wear. Pay close attention to the bolt face, extractor, ejector, gas key, and cam pin.
Cleaning and Lubrication
Thoroughly clean and lubricate the BCG. Carbon buildup and fouling can significantly impact its performance. Use a solvent to remove carbon deposits and apply a high-quality lubricant to all moving parts.
Extractor Inspection
Inspect the extractor for proper function. Ensure it can freely move and engage with a cartridge rim. Check the extractor spring for signs of weakness. You can test the extractor spring by pushing the extractor back against the bolt face. It should spring back quickly.
Ejector Inspection
Inspect the ejector for proper function. Ensure it is not damaged and is properly spring-loaded. Push the ejector down into the bolt face. It should spring back quickly and smoothly.
Firing Pin Inspection
Inspect the firing pin for damage and ensure it moves freely within the bolt. Remove any carbon buildup and check for bending or breakage.
Gas Key Inspection
Inspect the gas key screws to ensure they are properly torqued and staked. Check for any signs of gas leaks around the gas key. Look for carbon residue indicating escaping gases.
Repairing Bolt Carrier Group Problems
Once you’ve identified the problem, you can proceed with the necessary repairs. This may involve replacing worn or damaged parts, cleaning and lubricating components, or re-staking the gas key.
Replacing the Extractor
To replace the extractor, you’ll need to remove the extractor pin. Use a punch that is the correct size to drive the pin out. Be careful not to damage the bolt. Once the pin is removed, the extractor and extractor spring will come out. Install the new extractor and extractor spring, and then reinstall the extractor pin.
Replacing the Ejector
Replacing the ejector involves removing the ejector retaining pin. Again, be sure to use the proper sized punch. Once the pin is removed, the ejector and ejector spring will come out. Install the new ejector and ejector spring, and then reinstall the ejector pin.
Replacing the Firing Pin
Replacing the firing pin is a simple process. Simply remove the firing pin retaining pin and the firing pin will slide out. Install the new firing pin and retaining pin.
Re-Staking the Gas Key
Re-staking the gas key requires a staking tool. After properly torquing the gas key screws, use the staking tool to displace metal around the screws, preventing them from loosening.
Testing and Verification
After completing any repairs, it’s crucial to test and verify the functionality of the bolt carrier group.
Function Testing
Manually cycle the action to ensure smooth operation. Check for proper extraction, ejection, and chambering.
Live Fire Testing
Conduct live fire testing to confirm reliable performance. Load a magazine with ammunition and fire several rounds, observing for any malfunctions.
Conclusion
The AR-15 bolt carrier group is a critical component that requires regular maintenance and inspection. This article has provided a comprehensive guide to diagnosing and repairing common BCG failures. By understanding the function of each component, recognizing potential issues, and implementing effective solutions, you can ensure your AR-15 remains reliable and performs optimally. Keeping your AR-15 properly maintained and running is key to safe and reliable shooting.
By mastering these skills, you’ll not only save money on gunsmithing fees but also gain a deeper understanding of your AR-15 rifle. This knowledge empowers you to maintain your rifle in top condition, ensuring its reliable performance for years to come. This will also help to enhance your understanding of the entire platform.
As we continue our Gunsmith series, we will dive into other aspects of AR-15 maintenance and customization, as well as explore other types of firearms. In Gunsmith Part Seventeen, we will cover troubleshooting common magazine-related AR-15 malfunctions. We encourage you to share your experiences and questions in the comments below.
