The Sig Sauer MCX

Published on August 27, 2018
Duration: 51:27

This guide details the process of changing the barrel on a Sig Sauer MCX, allowing for caliber conversions between 5.56mm and 300 Blackout, and outlines the disassembly and reassembly of the updated bolt carrier group following a mandatory recall. It emphasizes the use of a specific torque wrench for barrel installation and highlights the safety features of the new bolt carrier group, including a captive firing pin retaining pin and a firing pin safety. The process is presented as achievable by an intermediate gunsmith or mechanically inclined individual.

Quick Summary

The Sig Sauer MCX bolt carrier group recall was due to a specific ammunition type prone to slam-fire, not a firearm defect. The updated carrier features a captive firing pin retaining pin and a firing pin safety for enhanced reliability and safety. Its barrels are easily swappable for calibers like 5.56 NATO and 300 Blackout using a torque wrench set to 60 inch-pounds.

Chapters

  1. 00:06Introduction to MCX
  2. 00:32Bolt Carrier Recall Overview
  3. 00:43MCX Design Origins
  4. 01:26Design Changes
  5. 02:03Designers Robert Hurt & Chris Royston
  6. 03:32Short-Stroke Piston System
  7. 03:54Changeable Barrel System
  8. 04:32Handguard and Rail System
  9. 05:25Receiver Construction
  10. 05:41Barrel Treatment (Nitride)
  11. 06:30From Butt to Muzzle Overview
  12. 07:07Stock Options
  13. 08:03Stock Removal Process
  14. 09:31Preferred Stock Configuration
  15. 10:25AR-15 Stock Adapter
  16. 10:41Lower Receiver Features
  17. 11:06Pistol Grip and Trigger
  18. 11:35Receiver Tensioner
  19. 12:05Safety Selector Design
  20. 12:38Magazine Release and Bolt Catch
  21. 13:01Ambidextrous Features
  22. 13:21QD Attachment Points
  23. 13:34Receiver Internals
  24. 13:53Rate of Fire and Development Challenges
  25. 14:26Machining Quality
  26. 14:42Upper Receiver and Charging Handle
  27. 15:42Forward Assist and Dust Cover
  28. 16:05Cam Pin Block Insert
  29. 16:46Handguard Removal
  30. 17:00Gas Valve Adjustment
  31. 17:43Barrel Swap Mechanism
  32. 18:05Torque Wrench Recommendation
  33. 18:24Barrel Swap Demonstration
  34. 18:51Barrel Gas Port Evolution
  35. 20:36Barrel Reinstallation
  36. 21:15Caliber Options (7.62x39)
  37. 22:02Barrel Lengths and Tax Stamps
  38. 22:16Handguard Reinstallation
  39. 22:27Gas Block and Twist Rate
  40. 22:51Bolt Carrier Group Overview
  41. 23:03Original vs. Modified BCG
  42. 23:10Reason for Recall (Slam Fire)
  43. 24:01Ammunition Manufacturer Issue
  44. 24:13Primer Types and Safety
  45. 25:19Sig's Customer Consciousness
  46. 25:55BCG Differences Detailed
  47. 26:04BCG Disassembly Process
  48. 26:34BCG Maintenance
  49. 26:50Recoil Spring Removal
  50. 27:05Carrier Disassembly
  51. 27:34Bolt Disassembly
  52. 28:26Original 300 Blackout Gas System Design
  53. 28:46Bolt Compatibility
  54. 29:04Recall Bolt Carrier Group Details
  55. 29:17BCG Differences: Operating Rod
  56. 29:40BCG Differences: Firing Pin Safety
  57. 30:11Aftermarket Trigger Compatibility Issues
  58. 30:39Milspec Trigger Design
  59. 30:44Geissele Trigger Update
  60. 31:07BCG Rear Assembly Disassembly
  61. 31:41Firing Pin Safety Mechanism
  62. 32:00Firing Pin Safety Disassembly
  63. 32:30Firing Pin and Retaining Pin
  64. 33:18Operating Rod Removal
  65. 33:33Bolt Modifications
  66. 34:11BCG Differences Summary
  67. 34:34New Gen 2 BCG Assembly
  68. 35:43BCG Reassembly Complete
  69. 37:08Sig's Recall Compensation
  70. 37:19Recall Return Process
  71. 37:34Sig's Investment in Recall
  72. 37:48Rifle Reassembly
  73. 38:27MCX Accessories
  74. 38:43Included Magazine
  75. 38:59Sig MCX Multi-Tool
  76. 39:37Caliber Conversion Kit Accessories
  77. 39:42Recommended Torque Wrench
  78. 40:20Barker Torque Wrench Availability
  79. 40:31Stock Options Overview
  80. 40:44Pistol Configuration
  81. 40:49Flash Suppressor Removal
  82. 41:01Optic: Sig Romeo 7
  83. 41:26Optic: EOTech for 300 Blackout
  84. 41:49Iron Sights
  85. 42:13Modularity and Customization
  86. 42:24Sling Attachments
  87. 42:46Overall Design Assessment
  88. 42:49Recall Issue Clarification
  89. 43:11Personal Recall Experience
  90. 43:23Current Recall Status
  91. 43:38Reliability and Safety Enhancement
  92. 43:45Range Test Introduction
  93. 44:02300 Blackout Ammunition Test
  94. 45:48Subsonic 300 Blackout Test
  95. 46:24Modularity: 300 Blackout to 5.56 NATO
  96. 47:205.56 NATO Barrel Insertion
  97. 48:58Converted to 5.56 NATO
  98. 50:04Sig MCX System Summary
  99. 50:11Original Purpose and Design
  100. 50:21MCX as 300 BLK First Design
  101. 50:30Future Accessories Expectation
  102. 50:41M-LOK Handguard Expectation
  103. 50:46MPX Comparison
  104. 50:56Video Conclusion and Thanks

Frequently Asked Questions

What was the primary reason for the Sig Sauer MCX bolt carrier group recall?

The Sig Sauer MCX bolt carrier group recall was initiated due to a specific type of ammunition tested by Sig Sauer that was prone to slam-fire. This meant the inertia from the firing pin could cause the cartridge to detonate unintentionally when the bolt closed, posing a safety risk.

How does the updated Sig Sauer MCX bolt carrier group differ from the original?

The updated MCX bolt carrier group features a captive firing pin retaining pin, a firing pin safety mechanism to prevent unintended firing, and a stronger method for securing the operating rod. These changes were implemented to enhance safety and reliability, particularly in response to the slam-fire issue.

Can the barrel on a Sig Sauer MCX be easily changed for different calibers?

Yes, the Sig Sauer MCX is designed with a quick-change barrel system. By loosening two screws on the barrel clamp mechanism with a torque wrench set to 60 inch-pounds, the barrel can be removed and replaced with barrels of different calibers, such as 5.56 NATO or 300 Blackout, or different lengths.

What are the key design features of the Sig Sauer MCX?

The Sig Sauer MCX is a modular, short-stroke piston-driven rifle originally developed for 300 Blackout. It features a changeable barrel system, KeyMod handguard, ambidextrous controls, a drop-in lower receiver compatible with AR-15 platforms, and a nitride-coated, hammer-forged barrel.

Is the Sig Sauer MCX recall mandatory, and should owners participate?

Sig Sauer issued a mandatory recall for the MCX bolt carrier group. While the issue stemmed from specific ammunition and not a firearm defect, participating in the recall is recommended as it provides an enhanced and safer bolt carrier group, representing a reliability and safety improvement.

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