The Short and Long of It: Understanding AR Gas System Lengths

The length of an AR 15 gas system can greatly affect the rifle’s performance, reliability, and overall shooting experience.

Understanding AR gas system lengths and their specific purposes can help ensure that the rifle is set up for optimal performance.

In this blog, we will discuss the different lengths of gas systems available for AR-style rifles, including pistol, carbine, mid-length, and rifle-length.

What Is an AR-15 Gas System

One of the key features of the AR-15 is its gas operating system, which allows the rifle to function by harnessing the energy from the fired round to cycle the action.

The gas system is located above the barrel, and it consists of a gas block, a gas tube, and a gas key (on the bolt carrier group). When the rifle is fired, a small amount of the hot gases that are expelled from the barrel travel through a small hole in the gas block and into the gas tube.

These gases then travel through the gas tube and into the gas key, where they drive the bolt carrier group to the rear, which in turn causes the bolt to rotate and unlock from the barrel. This action then allows the spent cartridge to be extracted and a new round to be loaded into the chamber.

There are different types of gas systems used on AR-15 rifles such as direct impingement and piston. Direct impingement is the most common type of gas system used on AR-15 rifles and it directs the gas directly into the bolt carrier group.

The Piston gas system is an alternative to Direct impingement which uses a separate piston rod to cycle the action, Piston systems are generally considered to be more reliable and cleaner.

The benefits of the gas system in the AR-15 include a lightweight design and a more reliable operation compared to other types of operating systems.

Additionally, the gas system allows for customization options, such as adjustable gas blocks, which can be used to fine-tune the rifle’s performance based on the ammunition and environmental conditions.

How Does an AR-15 Gas System Work

The AR-15 gas system works by harnessing the energy from the fired round to cycle the action of the rifle. When a round is fired, a small number of hot gases are expelled from the barrel and travel through a small hole in the gas block, located above the barrel.

These gases then travel through the gas tube, which runs parallel to the barrel, and into the gas key, which is located on the bolt carrier group.

The gas key is essentially a small valve that directs the gases into the bolt carrier group, which is the part of the rifle that contains the bolt and bolt carrier. As the gases enter the bolt carrier group, they push it to the rear, causing the bolt to rotate and unlock from the barrel.

This action then allows the spent cartridge to be extracted and a new round to be loaded into the chamber.

The movement of the bolt carrier group is what powers the cycling of the action on the AR-15. As the bolt carrier group moves to the rear, it also pushes the operating rod, which is connected to the bolt carrier group, to the rear.

The operating rod then pushes the cam pin, which is located in the bolt carrier group, causing the bolt to rotate and unlock from the barrel.

AR15 Gas Tube Lengths: Pistol, Carbine, Mid Length, and Rifle

Choosing the right gas system length for an AR-15 is important for optimal performance and handling.

The four gas system lengths are Pistol, Carbine, Mid-length, and Rifle, each with its own set of benefits and drawbacks.

It’s essential to understand the differences between them before making a decision.

The gas system on an AR15 can be very confusing. The following video runs you through the different gas tube lengths, gas block diameter, buffer tube setup, and barrel lengths to run.

What’s the Best Gas System Length for My AR-15?

When it comes to building or customizing an AR-15, one of the decisions you’ll need to make is the length of the gas system. The gas system length determines how much of the barrel is covered by the gas block and how much of the barrel the gas tube will run along. The two most common lengths are carbine length and mid length.

A carbine length gas system is typically used on barrels that are between 14.5 inches and 16 inches in length. This length provides a good balance between reliability and weight, making it a popular choice for many shooters. The carbine-length gas system places the gas block closer to the chamber, which allows for a shorter, more compact rifle.

On the other hand, a mid length gas system is typically used on barrels that are between 16 inches and 18 inches in length. This length provides a longer dwell time for the gas which results in a softer recoil and less stress on the operating system, also providing a longer handguard space. This can make the rifle more comfortable to shoot, especially for those who shoot for extended periods of time.

Ultimately, the best gas system length for your AR-15 will depend on your individual needs and preferences. If you’re planning to use your rifle primarily for close-quarters combat or home defense, a carbine-length gas system might be a good choice.

On the other hand, if you’re planning to use your rifle primarily for long-range shooting or competition, a mid-length gas system might be a better choice.

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