For starters, you’ll know pretty quickly if the gas system isn’t working properly on your AR. The firearm may not cycle properly, or you may see premature wear.
In order to better understand the various types of gas lengths in your AR, we kinda need to explain what the gas system does in the first place.
Gas System Explained:
When you look at your AR barrel, you’ll see a tiny hole on one side. That’s the gas port. When a bullet is fired through the chamber of the barrel, the gas from the bullet being fired is forced through the gas port via the gas block and directed down the gas tube and into the upper receiver.
The gas is then used to power the bolt carrier and cycle the next round. This is known as “direct impingement”.
In most instances, the longer the barrel, the longer the gas system. Most 7″ barrels (and shorter) have a pistol-length gas system. Most 16″ barrels have a carbine-length gas system. Most 18″ barrels have a mid-length gas system. Most 20″ barrels and longer have a rifle-length gas system.
However, you will occasionally see terms like “SOCOM” on a barrel, typically used to describe a 16″ barrel with a mid-length gas system.
What Difference Does It Make?
The length of the gas system affects both the smoothness of the firearm’s cycling of each round, and it’s dwell time.
Dwell time is the term used for the amount of time a bullet is in the barrel after the gun has been fired.
Typically, the longer the barrel, the harder the gas system has to work in order to get enough air to cycle the next round.
It should also be noted that, the longer the gas system (for example, the SOCOM barrel mentioned above), the more air is being pushed through. The longer the gas system, the smoother the cycling. Smoother cycling can positively affect the overall performance of the firearm.
It should be noted that, as in life, too much gas is a bad thing. If your gas port has been expanded and too much gas is being pushed through the system, then recoil and premature wear will be a factor. Always let a qualified gunsmith work on your gas ports – it can ruin the barrel if you make a mistake here!
So What Gas System Should I Have?
As with most AR-related questions…it depends. It depends on your barrel length, what distance you’ll be shooting, and what you’ll be using the AR for. And anyone who tells you that they have a magical, mystical system for gas lengths without knowing all of the answers to the variations mentioned above are probably trying to sell you a barrel.
A lot of it has to do with the barrel itself (see the entire series we did on AR barrels), but remember that this is an entire system with each part feeding off the other part, so changing one piece changes everything.
The best thing to do with ANY AR is to change one piece at a time to make sure the gun does what you want. Especially if you’re troubleshooting a gas system issue and not just wanting to lengthen the gas system for smoother cycling.
Have a question for the gunsmith? Wanna know something about your AR? Submit your questions via our Questions/Comments page or email us at firstname.lastname@example.org.