How Does it Work: Blowback Action

Published on January 10, 2019
Duration: 3:38

This guide explains the blowback operating principle in firearms, drawing on expert analysis from Ian McCollum of Forgotten Weapons. It details how Newton's Third Law governs the action, emphasizing the importance of the cartridge case seal and the mass-velocity balance for safe operation. The guide highlights practical applications and limitations of blowback systems, referencing specific firearms like the Colt 1903 and MP18.

Quick Summary

The blowback firearm action operates on Newton's Third Law, where the bullet's forward momentum is balanced by the rearward movement of the slide or bolt. The cartridge case expands to seal the breech, and a critical mass-velocity balance ensures the slide remains closed until pressure drops, making it ideal for lower-power cartridges.

Chapters

  1. 00:00Introduction to Blowback Action
  2. 00:32The Role of the Cartridge Case
  3. 01:11Physics of Safe Operation
  4. 02:19Practical Applications and Limitations

Frequently Asked Questions

What is the fundamental principle behind the blowback firearm action?

The blowback action operates on Newton's Third Law: for every action, there's an equal and opposite reaction. The forward momentum of the bullet is balanced by the rearward movement of the slide or bolt, which cycles the firearm.

Why is the cartridge case important in a blowback system?

During firing, the brass cartridge case expands to create a gas-tight seal at the breech. This prevents dangerous high-pressure gases from escaping while the bullet travels down the barrel and pressure is at its peak.

What is the 'mass-velocity balance' in blowback firearms?

This refers to the relationship between the weight (mass) of the slide or bolt and the speed (velocity) at which it moves. The slide must be heavy enough to remain closed until the bullet leaves the barrel and chamber pressure drops to a safe level.

What are the limitations of a pure blowback operating system?

Pure blowback systems are best suited for lower-power pistol cartridges. High-power rifle cartridges would require impractically heavy bolts or slides, making other operating systems like delayed blowback more suitable for such applications.

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