How Does it Work: Open Bolt vs Closed Bolt Firearms

Published on January 3, 2019
Duration: 4:36

This guide explains the fundamental differences between open bolt and closed bolt firearm operation, drawing on expert insights from Ian McCollum of Forgotten Weapons. It covers how each system functions, their respective advantages and disadvantages regarding accuracy and heat management, and touches upon manufacturing simplicity and historical US regulatory actions impacting semi-automatic open bolt designs. Understanding these mechanics is crucial for appreciating firearm design and function.

Quick Summary

Open bolt firearms hold the bolt rearward until the trigger is pulled, then cycle forward to chamber and fire, common in machine guns for cooling and preventing cook-offs. Closed bolt firearms have a round chambered with the bolt forward, offering better first-shot accuracy but potentially retaining more heat. The ATF banned new semi-auto open bolt production in the US due to conversion concerns.

Chapters

  1. 00:00Open Bolt Definition
  2. 00:21Closed Bolt Definition
  3. 00:33Action and Firing Modes
  4. 01:14Advantages of Open Bolt Systems
  5. 02:17Accuracy and Closed Bolt Advantages
  6. 03:11Manufacturing and Legal Status

Frequently Asked Questions

What is the primary difference between an open bolt and a closed bolt firearm?

In an open bolt system, the bolt stays rearward until the trigger is pulled, then moves forward to chamber and fire. In a closed bolt system, a round is already chambered, and the bolt is forward; the trigger releases a hammer or striker.

Why are open bolt designs common in machine guns?

Open bolt designs prevent 'cook-offs' (unintentional firing from heat) and allow for better cooling of the chamber between firing bursts because the chamber remains empty until the bolt cycles forward.

Which type of bolt system generally offers better accuracy?

Closed bolt systems typically provide higher first-shot accuracy. This is because the bolt's forward momentum in an open bolt system can slightly shift the firearm's aim at the moment of firing, whereas a closed bolt system's firing mechanism involves less overall movement.

Are there any legal restrictions on open bolt firearms in the US?

Yes, in the early 1980s, the ATF banned the new production of semi-automatic firearms that operate from an open bolt. This was due to concerns that such designs could be more easily converted to fully automatic fire.

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