Blowback facts for kids

Blowback is a clever way that some self-loading firearms work. Imagine a gun that can load its next bullet all by itself after you fire. Blowback is one of the main ways this happens!

When a bullet is fired, hot gases push it forward out of the barrel. But these gases also push backward on the empty cartridge case. In a blowback system, this backward push is used to move a part called the bolt (which holds the cartridge in place). This movement helps eject the empty case and load a new bullet into the chamber, getting the gun ready to fire again.

There are different types of blowback systems, but they all use this basic idea of gas pressure pushing the cartridge case backward. Most blowback guns don't have the bolt locked tightly when the gun fires. Instead, the weight of the bolt and a spring (called the recoil spring) are heavy enough to keep the gun closed until the bullet has left the barrel. This delay is super important for safety!

What is Simple Blowback?

Simple blowback is the most basic type of blowback system. Here, the backward push from the fired cartridge is enough to move the bolt all the way to the back. This action ejects the spent (empty) cartridge and allows a new one to be loaded.

You'll often find simple blowback in smaller firearms like automatic pistols and submachine guns. These guns usually fire cartridges that don't create extremely high pressure. For example, many 9mm pistols use simple blowback. Rifle cartridges, which create much higher pressure, are usually too powerful for simple blowback. If used, the bolt would open too quickly, which could be dangerous.

How Does Delayed Blowback Work?

Delayed blowback is a more advanced type of blowback. It's designed to handle the higher pressures of more powerful cartridges, like those used in rifles. The main idea is to "delay" the opening of the bolt just long enough for the pressure inside the gun's barrel to drop to a safe level after firing. This makes it safe to open the bolt and reload.

There are several clever ways engineers have created this delay:

Lever Delayed Blowback

In a lever delayed blowback system, there's a special lever connected to the bolt. When the gun fires, this lever slows down the bolt's movement at first. However, it also speeds up another part called the bolt carrier. Once the initial delay is over, the bolt then catches up and moves quickly with the bolt carrier to complete the reloading cycle.

• Examples: The French AA52 machine gun and the FAMAS assault rifle use this type of system.

Roller Delayed Blowback

Roller delayed blowback uses small rollers to create the delay. When the bolt moves forward to load a cartridge, these two rollers pop out from the sides of the bolt. They fit into special cutouts in the gun's receiver (the main body of the gun), effectively "locking" the bolt in place. When the gun fires, the pressure pushes the bolt backward. This pressure first forces the rollers inward, which takes a moment and slows down the bolt's opening. Once the rollers are fully retracted, the bolt can move freely to reload.

• Examples: Famous firearms like the Sturmgewehr 45 assault rifle, the Heckler & Koch MP5 submachine gun, and the Calico submachine gun use this reliable system.

Primer Actuated Blowback

Primer actuated blowback is a unique method where the primer itself helps unlock the bolt. The primer is a small, sensitive part at the base of a cartridge that ignites the gunpowder. In this system, when the gun fires, the primer moves backward slightly. This small movement pushes a firing pin (or a similar part) backward, which then unlocks the bolt. Once unlocked, the bolt can move freely to eject the empty case and load a new one.

• Examples: The Garand Model 1919 and the Postnikov APT are examples of firearms that have used this interesting blowback method.