Fail Zero AR-15 BCG Autopsy

Published on February 12, 2020
Duration: 13:25

This video provides an in-depth autopsy and inspection of a Fail Zero AR-15 Bolt Carrier Group (BCG) that was causing cycling issues. The instructor meticulously tests various components, including gas rings, firing pin protrusion, extractor, and carrier key integrity. The primary cause of failure was identified as a loose carrier key with poorly torqued screws and debris preventing a proper seal, rather than internal dimensions.

Quick Summary

A loose carrier key is a common cause of AR-15 cycling failures, leading to significant gas leakage. Inspecting for this involves checking for wiggle and performing a reverse torque test on the screws. Debris or improper torque can prevent a proper seal, rendering the BCG ineffective.

Chapters

  1. 00:00Introduction & Problem Statement
  2. 00:48Visual Inspection & Disassembly
  3. 01:14Gas Ring Test
  4. 01:51Bolt Tail Inspection
  5. 02:09Magnetic Test
  6. 02:25Gas Key Blockage Check
  7. 03:01Firing Pin Hole Test
  8. 03:12Firing Pin Protrusion Measurement
  9. 03:47Firing Pin Retaining & Cam Pin Check
  10. 03:54Extractor Gauging
  11. 04:33Carrier Key Bore Gauging
  12. 05:43Gas Ring Run Test
  13. 06:17Bolt Tail Interface Test
  14. 07:17Carrier Key Loose Check
  15. 07:45Carrier Key Screw Torque Test
  16. 09:11Debris Under Carrier Key
  17. 10:25Root Cause Analysis: Loose Carrier Key
  18. 10:32Headspace Check
  19. 13:10Conclusion & Repair Recommendations

Frequently Asked Questions

What are the common causes of an AR-15 bolt carrier group (BCG) failing to cycle properly?

A primary cause for an AR-15 BCG failing to cycle is a loose carrier key, which leads to significant gas leakage. Other issues can include insufficient gas rings, blockages in the gas key, or problems with firing pin protrusion or extractor function, though a loose carrier key is often the most critical failure.

How can I test the gas rings on my AR-15 bolt carrier group?

You can test AR-15 gas rings by removing the firing pin and cam pin, then holding the bolt carrier upright. If the bolt itself falls out due to gravity, the gas rings are likely worn or insufficient. Another method involves removing the cam pin and holding the bolt face down, then shaking to see if it comes loose.

What is the correct firing pin protrusion for an AR-15?

The acceptable range for AR-15 firing pin protrusion is typically between .028 and .035 inches. This measurement is crucial for reliable ignition and preventing issues like slam fires or light primer strikes. It can be measured using a specialized depth or anvil gauge.

How do I check if the carrier key on my AR-15 BCG is loose?

To check for a loose carrier key on an AR-15 BCG, you can attempt to wiggle it by hand. A more precise method involves using a torque wrench set to approximately 20 inch-pounds and performing a reverse torque test on the carrier key screws. If they break free easily, the key is likely loose.

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