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The AR-15 Gas System

The AR-15 Gas System

November 05, 2018

As you research AR-15 accessories and upgrades, you will come across two gas systems: direct impingement or piston. These two gas systems are how the AR-15 fire, return the bolt, strip a new cartridge off the magazine, and chamber a new round. There are pros and cons to both, but a large majority of the AR rifle systems utilize the DI system. There are specific reasons why you would utilize a piston gas system, but you can decide which system you want to use after you read this article.

You will find two major types of gas systems for the AR-15:

  • Piston
  • Direct Impingement (DI)

What’s The Difference Between DI and Piston?

A large majority of ARs are direct impingement, which works as explained below.

Hot gas is directed from behind the bullet into the gas tube, where the gas is sent directly back to the chamber.

This results in the bolt unlocking and moving back, the casing expelling, and then stripping a new cartridge into the chamber.

The piston works in a similar fashion, but it does not involve sending the hot gas back to the chamber. Instead, the hot gas is used to effect a piston that initiates the unlocking, expelling, and stripping.

Piston Pros and Cons

If you’re considering a piston setup, here are some of the most common pros and cons to consider.

  • Costs more than a Direct Impingement System
  • Places more weight in front
  • Some parts are unique to manufacturer
  • Reduces accuracy


  • Gas is vented away, so the process is cleaner
  • Said to be more reliable when encountering dust, water, etc.
Overall, a Direct Impingement system will work just fine for your needs. If you’re shooting after being in water, dust, sand, or “rough” environments, you will want to consider a piston gas system.

Gas Block

The gas block is what utilizes the hot gas from firing the rifle and returning the bolt. For some, the “front sight base” (FSB) combines the front sight and the gas block into one component. For others, they prefer to use a gas block so that they can implement a free-floating rail.

You will find in the market low-profile gas blocks that better suit the customization of AR-15s. What’s more, some of these blocks are adjustable, which means you can control the amount of gas used.

For most, the desire to install a rail on their rifle means they want to skip the FSB and go straight for a gas block. Also, consider the type of barrel you are using to decide on which gas system best fits your needs.

Rail Scales: High-Quality AR-15 Accessories

Now that you understand the difference between a DI and a piston gas system, you can make the best choice when upgrading your rifle. For the most part, you will want to go with a DI system, but the choice is ultimately yours. In the meantime, give the Rail Scales AR-15 accessories a look to find your next upgrade. Shop online now!