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Piston Vs. Direct Gas Impingement Systems 3.67/5 (73.33%) 3 votes

1274inpostLet’s take a look at one of the most debated topics among AR-15 owners and enthusiasts: which system is better, direct gas impingement or piston impingement systems?  No matter what side of the debate you are on somebody, somewhere will have an argument against your choice system, and they may be right.  Both systems have their advantages and disadvantages.

It’s important to know the difference between the two, and they are both simple to understand.  Direct gas impingement forces gas down a tube in reverse direction to the projectile while piston systems use the same gas to force a piston mechanism.  Both systems are responsible for ejecting the casing by forcing the bolt back, so what’s the difference?

AR-15 Gas Impingement

Gas Impingement


Let’s talk about the gas system first.  The gas system was the introductory standard system when AR-15’s were first created.  In a gas system there is a gas block towards the end of your barrel that forces gas back towards the bolt ultimately using just pressure to force the bolt back.  As soon as the gas forces the bolt carriage back it escapes, your cartridge reloads and the bolt slides forward into place.


Source: Image is of an AK but the same idea is used in a piston AR

A piston system uses the same gasses (the gasses that force your bullet out the barrel) to force a piston back into the bolt to achieve the same action of chambering a new bullet.  Gasses in this system are expelled at about the same location as the gas block in the gas impingement system, hopefully, and well maintained systems will.

Pros & Cons

Now let’s talk pros and cons of the gas system.  These systems are typically best for individuals who won’t be firing thousands of rounds over the course of a weekend because in that case they are going to get dirtier; with the gas systems the “crud” or carbon is all forced back into the bolt and will build up quickly.  They are lighter than piston impingement systems since there is less metal in the rifle.  Gas impingement systems have less recoil as well, although avid shooters of both models will tell you that it is un-noticeable unless you are on the petite side, or have bad form.  Now, there are downsides to the original gas system.  The biggest downside as mentioned is that they get dirtier faster meaning that if you don’t feel comfortable cleaning your own rifle after about 500-600 rounds you may start to notice your gun’s ejection mechanism failing.

Piston systems have their own set of pros/cons.  They are typically better for anyone who will do a lot of training i.e. fire a ton of rounds.  They don’t get as hot as gas guns, and since gasses are expelled at the barrel’s end they won’t be discharged into your face.  Essentially they are better for the more tactical shooter.  They are also easier to convert to a civilian “legal machine gun”, although we’ll cover that later on. The downsides of piston guns are the extra parts, not many but still more than gas guns.  These parts could lead to maintenance you may not want to do yourself and they add extra weight.

All in all these guns are both good in their own rite, and if you’re reading this you probably own one or the other, or might be in that market.  Just remember, if the gun works for you then you have your answer.


Piston vs DI Dilemma: “The AR-15 Gas Choice”