Gas Impingement and Piston Operating Systems

Gas Impingement Is The Original Design For The AR Platform

Cutaway of part of an AR15 Gas Impingement System
Cutaway of part of an AR15 Gas Impingement System

Understanding How The AR15/AR10 Work

If you are going to own an AR15 or AR10, it helps if you understand how the rifle works. Ar15 style rifles come in two varieties; direct impingement and piston driven.  I am going to give you a brief explanation of both and share with you a great video from Vickers Tactical.

Direct Impingement

Direct Impingement is the original technology, devised the originator of the AR series rifle, Eugene Stoner, in the 1950s. Gas from the fired round is bled through a small hole located in the barrel. The gas is then channeled through a very small tube that goes directly to the bolt carrier. The gas is next pushed to the rear of the rifle, that causes the spent case to be extracted and ejected. The bolt carrier is then pushed forward by spring-loaded action from the buffer tube, and strips a new round from the magazine, loading it directly into the chamber of the barrel. This design was a radical change from gas pistons used in much earlier military rifles like the M-1 Garand.


While similar to impingement systems, there are significant differences. With the piston, the firing process begins in much the same way, as gas is bled from the barrel. However, instead of the gases being forced into a small tube, it is contained in a separate cylinder that contains a piston. The gas moves the piston, which turn pushes the bolt carrier rearward to handle the extraction and ejection process. The bolt carrier is then moved forward to the closed position by a spring just like in direct impingement.

In today’s market, you can get both. The argument for pistons is they are supposed to run cooler and get less dirty. The chief complaint with direct impingement is how dirty the bolt gets because the gas is directed back at it. Cleaning a rifle is an outcome you might delay but can never outrun. I have shot both and prefer to keep my ARs direct impingement as they were originally designed. If I want a piston rifle, I go to my standard AK-47 and shoot it as it was designed, but that’s only my opinion. I know people who swear by both systems.

Here is a great 5-minute video that will show exactly how gas impingement works. The video is badass.

Vickers Tactical AR15 Cutaway Video

If you’d like more information or have any questions, feel free to email me at Please remember that Live Free Armory is here to help you whether you choose to buy from us or not.  We believe that obtaining the right information should always be your first step.

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