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What is a Gas Block / Gas Tube?

The AR-15 is a semi-automatic gas-operated rifle, which means that it relies on the gas created by the firing of the bullet to reload the gun. To be more elaborate, the AR-15 has a direct gas impingement system, which may sound complicated, but is quite straightforward.

When the weapon is fired, the explosion of the bullet creates a lot of gas in the chamber, which propels a projectile through the barrel as the gas moves behind it. As the gas passes the gas port, some of it is redirected into the gas block. The gas then travels through the gas tube to the bolt carrier group, and the pressure created because of it bushes the bolt carrier back, ejecting the fired casing, and reloading a live round from the magazine.

Therefore, the gas block plays a very important role in the operation of the AR-15.

What Factors Affect the Functioning of the Gas block?

There are several factors that determine the performance of the gas block on your rifle. First of all, the length of the gas system is very important.  If the length of the gas system is too short, it can lead more gas into the receiver, increasing felt recoil and putting unnecessary wear on the bolt carrier group, buffer spring, and the gas tube itself.

On the other hand, if the gas system is too long, and it doesn’t let enough gas into the receiver, then you could face reliability issues and run into malfunctions like stove pipes, failure of feed, and failure to eject. Therefore, finding the right length for the gas block is very important.

The ammunition also affects the functioning of the gas system. Heavier loads create more gas, whereas subsonic rounds create less gas. In some situation, using a suppressor can also increase the gas pressure

Types of Gas Blocks on AR-15s:

In general, there are three types of gas blocks that can be used with AR-15s. First of all, we have the low profile gas block. These gas blocks are regarded as the best for high end AR-15s, and one of their best advantages is that they can work with almost any free float handguard. Moreover, these gas blocks can be installed at different lengths, unlike the only FSB gas blocks.

FSB or front sight block gas blocks are embedded into the front sight block and therefore, are always a standard length, you can find these gas blocks on most military M4s, and military style AR-15s.

Lastly, you can also use an adjustable gas block on your AR-15. These blocks are really good because they allow you to control how much gas makes it into the receiver. They are mostly used with AR pistols, since they have shorter barrels and hence shorted gas tubes.

What happens if the gas block stops working?

Though the gas block is a very important part of the AR-15 rifle, you can still fire it if the gas system fails. However, your rifle will essentially operate as a bolt action rifle, where you will have to manually pull the charging handle to load every round into the chamber.


Gas Block, Gas Tube

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