Author Topic: The Perfect AR Gas System?  (Read 2626 times)

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Online Elderberry

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The Perfect AR Gas System?
« on: April 16, 2019, 02:40:33 pm »
Primary Arms

GAS SYSTEM GUIDE

Whether you go with a gas piston conversion or a traditional gas tube for your AR-15, deciding what gas system length is the right option for you can be a confusing process. With several options to choose from, in seemingly limitless barrel configurations, it’s easy to get lost. Today we’ll be looking at the most common lengths for AR-15 gas systems and we’ll cover the pros and cons of each to help you make an informed decision.


Gas system length and effects don’t change between DI or piston driven.

What does the gas system do?
The AR-15 is a gas operated firearm with a multi-lug rotating bolt that fires from a locked breach. Let’s break this down. When firing, the bolt is locked into the barrel extension. To operate and cycle the action, the rifle will use some of the high-energy gas that propels the bullet down the barrel to push the bolt carrier back, unlock the bolt, and extract the empty casing. As the bolt carrier group moves rearward and the casing is ejected, the buffer and buffer spring inside the stock assembly will absorb the energy and push the bolt and carrier back forward. As this happens, the carrier strips a new round from the magazine, feeding it into the chamber, and then locking the bolt lugs back into the barrel extension so the rifle is ready to fire again.

With a standard AR-15 the gas that makes this all happen is fed through the gas port (a small hole drilled into the top of the barrel), into the gas block, and then down the gas tube. The gas tube enters the upper receiver and feeds into the gas key on the bolt carrier. Inside the bolt carrier group, that gas fills a small piston chamber inside of the bolt carrier formed by the tail of the bolt, which pushes the carrier backwards. This causes the bolt to rotate and unlock, allowing the action to cycle again. Alternatively, a gas piston-driven rifle feeds gas through the same gas port and gas block arrangement as a standard AR-15, but instead of pushing the gas through the gas tube to cycle the bolt, it pushes an external piston instead, and that piston’s displacement moves the bolt carrier to cycle the rifle. For this article, we are referencing the more common direct impingement system with a gas tube, but the information on gas system lengths and their advantages or weaknesses will hold true for both options
Pick Your System
Whether you want to use a gas piston or a traditional direct impingement gas system for your AR-15, it is important to know the “why” behind the different gas system lengths. Today we’ll be looking at the four most common gas system lengths you’ll find, how to identify them, and how they can meet the needs of your build. Longest to shortest, they are: Rifle, Mid-length, Carbine, and Pistol. The longer the system, the further away from the receiver the gas port and gas block will be located down the barrel. Where the gas port is located has a drastic effect on a rifle’s reliability and felt recoil, as well as long-term parts durability. This is because more or less gas pressure is available to cycle the rifle depending on the length of system. For the purposes of this article, we’ll be treating these gas systems as ‘all else being equal’ and ignoring the various buffer weights and systems, which also influence recoil, reliability, and parts durability. Before we get into it, let’s take a quick look at a few terms that are going to pop up going forward:

Gas Port Length: Distance from the face of the upper receiver to the center of the gas port

Gas Tube Length: Length of gas tube (for standard direct impingement AR-15s). This is a rough measurement; some minor variance is expected and normal.

Dwell Time: Amount of time the bullet has to travel through the barrel before the action begins to cycle.

Now: Let’s get into it.

More: http://news.primaryarms.com/q/AgdgdO344YJz9ZKdsdBedh7wtnVpwiztVzmtg4DnDKdFlSMQM09Lr5QDg


Offline verga

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Re: The Perfect AR Gas System?
« Reply #1 on: April 25, 2019, 11:26:42 pm »
My AR has 24 inch barrel so i have to use the Rifle length tube. According to this article I am 6 inches over the "ideal length". Mine has performed flawlessly and eats darn near anything I give it without a single hiccup.
In a time of universal deceit - telling the truth is a revolutionary act.
�More than any other time in history, mankind faces a crossroads. One path leads to despair and utter hopelessness. The other, to total extinction. Let us pray we have the wisdom to choose correctly.�-Woody Allen
If God invented marathons to keep people from doing anything more stupid, the triathlon must have taken him completely by surprise.

Online Elderberry

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Re: The Perfect AR Gas System?
« Reply #2 on: April 26, 2019, 12:02:19 am »
My AR has 24 inch barrel so i have to use the Rifle length tube. According to this article I am 6 inches over the "ideal length". Mine has performed flawlessly and eats darn near anything I give it without a single hiccup.
@verga

The ideal length for the Rifle Gas System was listed as 18"+ so you haven't exceeded the "ideal length".

Now my 358Yeti does as I have an 18 inch barrel with a Carbine Gas System with an "ideal length" of 10.5” - 16”.

Offline verga

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Re: The Perfect AR Gas System?
« Reply #3 on: April 26, 2019, 11:31:40 am »
@verga

The ideal length for the Rifle Gas System was listed as 18"+ so you haven't exceeded the "ideal length".

Now my 358Yeti does as I have an 18 inch barrel with a Carbine Gas System with an "ideal length" of 10.5” - 16”.
Got it. Thanks
In a time of universal deceit - telling the truth is a revolutionary act.
�More than any other time in history, mankind faces a crossroads. One path leads to despair and utter hopelessness. The other, to total extinction. Let us pray we have the wisdom to choose correctly.�-Woody Allen
If God invented marathons to keep people from doing anything more stupid, the triathlon must have taken him completely by surprise.