Semi-Automatic Gun

How Does A Semi-Automatic Gun Work?

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Semi-Automatic Gun Works

The history of semi-automatic guns can be traced back to 1885. The 85 was the first successful design of a semi-automatic rifle by a gunsmith from Australia named Mannlicher. Over many decades, the gun industry and specifically semi-automatic firearms have experienced enormous development. A lot of innovation has been applied to improve and enhance the functioning of semi-automatic guns. The types of operations used in semi-automatic guns include the blowback, recoil, and gas-operated guns. How a semi-automatic gun works? 

The below explanation will take you through each mode of operation of a semi-automatic firearm. 

How A Semi-Automatic Gun Works
How A Semi-Automatic Gun Works

Blowback Operated Guns

It’s among the simplest system of operation in semi-automatic guns. Basically, it applies Newton’s 3rd Law; therefore, there is an equal and opposite reaction for every action. 

How does a blowback operate gun work? The action of the bullet moving down the barrel is balanced when the slide or the bolt of the gun moves backward. It involves balancing the momentum of the bullet with the amount of mass going back.  

In many instances, this system functions very well with pistols caliber cartridges and low power cartridges. 

However, some guns chambered for more powered cartridges use a different variation called delayed blowback operation. Unlike simple blowback, delayed blowback has a better mechanism of resistance to action opening, thus increasing the bolt’s effectiveness. As a result, it facilitates a decrease in gas pressure, thus minimizing operating pressure. 

Delayed blowback is in two forms, i.e., Lever Delayed Blowback and Roller Delayed Blowback.

Lever-Delayed Blowback system

A Lever-Delayed Blowback system is not very common but has been utilized in rifles, submachine guns, and light machine guns. It involves applying the mechanical disadvantage principle on the fulcrum lever, thus forcing a speedup of mass on the rear side as the bolt remains closed. As a result, there is an amplified weight of moving parts of a firearm. 

Roller-Delayed Blowback system

The Roller-Delayed Blowback system is similar to the roller –locked system. However, it uses an angled locking wedge to apply mechanical disadvantage on rollers to restrain bolt movement but allow carrier movement rearward. As a result, there is delayed action from opening until pressure is minimal at a safer level. Conversely, for reliable extraction, you need to use chamber fluting. 

Recoil Operated Guns

Another operation of semi-automatic firearms is the recoil operation. Generally, firearm under this category is known to have a recoil impact. They use that recoil energy to operate the action of a gun. When you pull the trigger, the hammer will hit the primer to drive the bullet through the barrel. As a result, energy produced pushes the slide, and the barrel moves backward to eject the cartridge, and the forward movement will lead to the chambering of another round. Recoil operation is of three types, i.e., short recoil, long-recoil, and inertia. 

Long Recoil-operated Guns

When you fire a gun that is long-recoil operated, the recoil energy generated causes the bolt and barrel to move rearward. The returning spring forces the barrel to unlock and move forward while the ejector eliminates the cartridge case. When the barrel is back to its firing position, the bolt is released while the second spring feeds in the chamber with another round. Long recoil-operated gun tends to be mechanically complex and has a higher recoil effect than normally felt recoil. 

Short Recoil-operated Guns

On the other hand, short recoil-operated guns utilize the slide instead of the bolt, so they are usually pistols. The slide and the barrel are locked together but a smaller distance as they move backward. As a result, the empty case comes out through the ejection port, and also the recoil spring is compressed. Also, it causes the slide to get back to a firing position as another round from the magazine is chambered. 

Inertia Recoil-Operated Guns

Inertia recoil-operated firearms have a two-piece bolt that is separated by a beefy spring. When the bolt comes back to position, the bolt head rotates up into action. Also, a recoil causes the spring between the bolt pieces to compress as a way to gather enough energy to launch the bolt backward. A rearward movement of the bolt ejects the empty case. While going back to the battery, the bolt springs are uncompromised and come along another round. 

Gas Operated Guns 

Other semi-automatic forearms use a gas-operated system. When you pull the trigger, and a cartridge is fired, the bullet starts to propel down the barrel. The bullet will continue moving with the help of specialized gasses that enhance action in such a gun. It involves directing gas from the fired cartridge towards and in the bolt carrier. There is a port on the barrel near the chamber where gas escape through it to initiate movement.

When the gas comes out, it pushes against the piston attached to the bolt carrier. As a result, the bolt carrier will move backward, unlocking the bolt. Then the spent cartridge is eliminated, and assembly moves forward; it picks up another round from the magazine and chamber it. Finally, the bolt locks in place, ready to fire the chambered round. 

Gas operated gun are also of different forms, i.e., long-stroke piston and short-stroke piston. The long-stroke piston guns have pistons connected to the bolt carrier group. The short strike piston guns do not have their pistons connected to the bolt carrier group. 


Semi-automatic firearms are common among many shooters. However, they are of different variants and works differently. It’s also worth noting that there are other semi-automatic gun operations but are not very common, and thus they are less adopted. 

Semi-automatic guns are easy to use and handle, yet they require proper cleaning and maintenance. 

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