Knights Armament Company Sandcutter AR BCG Autopsy

Published on February 15, 2020
Duration: 15:30

This video provides a detailed autopsy of a Knights Armament Sandcutter AR Bolt Carrier Group (BCG) that was causing reliability issues. The instructor systematically disassembles and inspects each component, including the bolt, extractor, firing pin, cam pin, and carrier bore, using various gauges and tools to identify potential problems. The primary finding is a broken gas key fastener, which is identified as the cause of gas leakage and the firearm's failure to cycle.

Quick Summary

The Knights Armament Sandcutter AR Bolt Carrier Group failed to function due to a broken gas key fastener, causing significant gas leakage. This was identified during a detailed autopsy involving component inspection, gauging, and torque testing of the gas key screws.

Chapters

  1. 00:00Introduction and Problem Statement
  2. 01:04Disassembly: Firing Pin, Cam Pin, Bolt
  3. 01:24Extractor Inspection
  4. 02:01Cam Pin and Firing Pin Inspection
  5. 02:15Firing Pin Protrusion Check
  6. 02:34Bolt Retaining Pin and Lug Inspection
  7. 03:02Extractor Claw and Spring Test
  8. 03:06Magnetism Test
  9. 03:25Gas Key Bore Path Check
  10. 03:46Gas Key Alignment Check
  11. 04:11Bolt Firing Pin Hole Gauge Test
  12. 04:20Ejector Inspection
  13. 04:48Bolt Tail Dimension Check
  14. 04:59Gas Ring Test
  15. 05:20Cam Pin and Roll Pin Check
  16. 05:29Bolt Face Inspection
  17. 05:40Gas Rings Condition
  18. 05:40Headspace Check
  19. 06:21Carrier Bore Gauging
  20. 06:39Gas Key Screw Torque Test
  21. 11:13Discovery of Broken Gas Key Fastener
  22. 12:04Analysis of Broken Fastener Cause
  23. 13:44Visual Confirmation of Broken Fastener
  24. 14:14Conclusion and Next Steps

Frequently Asked Questions

What was the primary reason the Knights Armament Sandcutter BCG was not functioning?

The primary reason the Knights Armament Sandcutter BCG was not functioning was due to a broken gas key fastener. This breakage caused significant gas leakage, preventing the firearm from cycling properly.

How are gas key screws tested for tightness in a BCG autopsy?

Gas key screws are tested for tightness using a reverse inch-pound torque tester. An initial check is performed at 20 inch-pounds, and if that passes, it can be moved up to a maximum of 30 inch-pounds for testing.

What are the key components inspected during a BCG autopsy?

During a BCG autopsy, key components inspected include the firing pin protrusion, extractor claw and spring tension, cam pin, bolt tail dimensions, gas rings, bolt face for erosion, and the carrier bore for proper fitment using gauges.

Can a BCG with a broken gas key fastener be repaired?

A BCG with a broken gas key fastener typically requires replacement of the gas key. The broken fastener must be extracted, and a new gas key installed and properly staked.

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