Why is this Sten MK.II full of holes? With firearms expert Jonathan Ferguson

Published on November 8, 2023
Duration: 13:29

This video provides an in-depth look at the Sten MK.II submachine gun, focusing on its simple blowback operating system. Firearms expert Jonathan Ferguson explains how the heavy bolt and recoil spring manage the firearm's cycle of operation. He details the function of the sear and the tripping lever (disconnector) in enabling both full-automatic and semi-automatic fire, using a cutaway example for clarity.

Quick Summary

The Sten MK.II submachine gun operates on a simple blowback system, utilizing a heavy bolt and recoil spring. A sear holds the bolt back, and releasing it initiates the firing cycle. For semi-automatic fire, a tripping lever (disconnector) disconnects the trigger from the sear after each shot, preventing continuous firing.

Chapters

  1. 00:00Introduction: Sten MK.II Cutaway
  2. 00:34Jonathan Ferguson Introduces the Sten MK.II
  3. 01:34Simplicity of Automatic Fire: Blowback System
  4. 02:06Key Components: Bolt and Spring
  5. 02:24Blowback vs. Locked Breech Systems
  6. 03:19Manual Operation of the Cutaway
  7. 03:55Fire Selector: Automatic (A) and Repetition (R)
  8. 04:30The Role of the Sear
  9. 04:34Etymology of 'Sear'
  10. 05:14Trigger Pull and Bolt Cycle
  11. 05:47Automatic Fire Explained
  12. 06:05Ease of Automatic vs. Semi-Automatic Design
  13. 06:32Bolt Ledge for Sear Engagement
  14. 07:17Visualizing the Sear Catch
  15. 07:37Cutaway for Semi-Automatic Fire
  16. 07:48Trigger Bar and Tripping Lever
  17. 09:10Semi-Automatic (Repetition) Mode
  18. 09:58Trigger Disconnection Mechanism
  19. 10:37Difference Between Automatic and Semi-Auto Trigger Function
  20. 11:31The Disconnector's Function
  21. 12:05Comparing Cutaway to World of Guns
  22. 12:31Call to Action: Like and Subscribe
  23. 12:41Visit Royal Armouries Museums
  24. 12:48History of Weapons and War App/Website

Frequently Asked Questions

How does the Sten MK.II achieve full-automatic fire?

The Sten MK.II uses a simple blowback system. When the trigger is pulled, the sear holding the bolt back is released. The bolt then slams forward, fires a round, and the resulting gas pressure blows the bolt back to compress the spring, ready to fire again. This cycle repeats as long as the trigger is held and ammunition is present.

What is the function of the sear in the Sten MK.II?

The sear is a critical component that holds the heavy bolt back in the receiver after it has cycled. When the trigger is pulled, the sear is disengaged, allowing the bolt to move forward and fire the next round, initiating the blowback cycle.

How does the Sten MK.II switch between automatic and semi-automatic fire?

The Sten MK.II uses a tripping lever (disconnector) for semi-automatic fire. In this mode, a ledge on the bolt interacts with the tripping lever after firing, disconnecting the trigger from the sear. This prevents continuous firing, allowing the sear to reset for the next trigger pull.

Why is the Sten MK.II easier to make as a full-automatic weapon?

The Sten MK.II's design is based on a simple blowback system, which is inherently easier to configure for full-automatic fire. Unlike locked-breech firearms that require complex mechanisms to lock the bolt, the Sten relies on the inertia of its heavy bolt and spring, making it simpler to produce for continuous fire, especially with pistol-caliber ammunition.

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