Military Life

Choosing an AR: Gas or Piston?

Despite the negative attention courteous of the media, AR style rifles are still one of the most popular platforms available. Whether you are looking to do some target practice, home defense or even hunting (if you live in a jurisdiction which allows it), chances are there is an AR model for you. But, because there are so many models and options available, selecting your first one can be as difficult as hitting your first running coyote. One of the first decisions you will need to make is which type of operating system you need – direct gas impingement or piston system.

Disclaimer – before going any further I want to state that I understand “AR” does not stand for “automatic rifle” or “assault rifle”, nor does it technically address every model by every manufacturer out there. By strict standards, “AR” stands for “ArmaLite Rifle” – originally designed by the ArmaLite Company and later Colt Firearms. For the purpose of this article, I will break some rules by using this term as a general means of describing not only the original model but also the many model copies on the market.

AR-style sporting arms are available with your choice of two different operating systems – direct gas impingement or piston system. I will provide a basic description of each as well as the general pros and cons associated with the specific systems. Hopefully, this will assist you in determining which is best for you.

Direct Gas Impingement

With a direct gas system, a small amount of gas is redirected from the forward portion of the barrel into a small tube which runs the length of the barrel, after which it enters the chamber. This gas then drives the bolt carrier to the rear, allowing the weapon to cycle.

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  • Because it was used in the original design, it is often considered to have the most proven track record; all the bugs have been worked out long ago.
  • Reliability due to less complicated system utilizing less moving parts.
  • Easy to work on with many parts being interchangeable between manufacturers.
  • Lightweight.
  • Cheaper to manufacture and purchase.


  • Very dirty to operate. Recycled gas entering the chamber also introduces large amounts of dirt and debris.
  • No adjustment available for gas delivery system – it’s all or nothing.
  • Hotter to operate.

Piston System

As with the direct gas impingement system, a small amount of gas is captured and redirected via a small tube. However, instead of entering chamber, the gas hits a rod/piston system which then drives the bolt carrier to the rear and cycles the weapon.


  • Much cleaner than the gas system due to reduced amount of gas coming in contact with the chamber.
  • System operates fast and weapon cycles quicker.
  • Ability to adjust gas pressure; a very handy feature if using a suppressor or attempting precision shots.
  • Cooler operating temperatures.


  • Heavier than gas system, generally by at least 1 lb.
  • High production cost means high sale price for consumer.
  • Most systems use a proprietary design specific to individual manufacturers, limiting the availability of after-market parts.


Each system has advantages and disadvantages and users who will swear by one or the other. Personally, I prefer the gas impingement design but realize that final selection is a very personal decision and understand why other shooters feel piston is the only choice for them. If you are new to the AR system, I recommend trying both and seeing which feels right for you.

Disclaimer: The content in this article is the opinion of the writer and does not necessarily reflect the policies or opinions of US Patriot Tactical.


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