JM940 Pro Disassembly with #JerryMiculek

Published on August 26, 2025
Duration: 11:10

This video provides a detailed, step-by-step guide on how to field strip and reassemble the Mossberg 940 JM Pro shotgun, led by firearms expert Jerry Miculek. It emphasizes safety, proper component handling, and critical reassembly steps, particularly concerning the magazine extension and gas system, to ensure reliable function. The instruction highlights the gun's user-friendly design for maintenance.

Quick Summary

To safely field strip the Mossberg 940 JM Pro, first ensure it's unloaded. Remove the magazine extension, handguard, and barrel assembly. Then, remove the bolt and trigger group. Pay close attention during reassembly, especially when reattaching the magazine extension, to ensure the tube contacts the fixed magazine, preventing spring-related feeding issues.

Chapters

  1. 00:00Introduction & Safety Check
  2. 00:34Magazine Extension Removal
  3. 01:11Handguard and Barrel Assembly Removal
  4. 01:39Pusher, Action Spring, and Follower Removal
  5. 01:55Bolt Removal
  6. 02:17Trigger Group Removal
  7. 03:13Receiver Cleaning & Component Overview
  8. 04:36Trigger Group Reassembly
  9. 04:47Bolt and Charging Handle Reassembly
  10. 05:11Handguard and Gas System Reassembly
  11. 05:49Barrel Reassembly
  12. 07:33Magazine Extension Reassembly Critical Steps
  13. 08:57Magazine Spring and Extension Cap Installation
  14. 10:34Final Checks and Conclusion

Frequently Asked Questions

How do you safely field strip a Mossberg 940 JM Pro shotgun?

Begin by ensuring the shotgun is unloaded, checking both the chamber and magazine. Remove the magazine extension, then the handguard. Lock the bolt to the rear, remove the barrel and gas piston assembly, followed by the bolt. Finally, remove the trigger group by pushing out its retaining pins, handling it carefully to avoid losing internal parts.

What are critical steps for reassembling the Mossberg 940 JM Pro's magazine extension?

When reassembling the two-piece magazine extension, it's crucial to screw the magazine tube down until it contacts the fixed magazine on the shotgun. This eliminates any void that could trap the magazine spring, preventing feeding malfunctions.

Why is the Mossberg 940 JM Pro's gas system considered durable?

The 940 JM Pro's gas system is durable because its gas piston, even at full stroke, remains contained within the cylinder. This design prevents gas rings from exiting the cylinder, significantly reducing wear on these components over time.

Are there any parts in the Mossberg 940 JM Pro that are considered consumable?

Yes, the magazine spring is considered a consumable item, especially in high-capacity shotguns like the 9-shot 940 JM Pro. It undergoes significant stress during recoil and feeding cycles and will eventually take a set, requiring replacement for reliable function.

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