AR15's: Gas system question

[Harold Mayo]

While I've been shooting ARs for years, I've only varied twice from a 16" barreled gun with a carbine-length gas system. On the two occasions that I departed from that, I have no recollection of any difference to answer my question so I submit to the forum the following question:

Is a longer gas system than the carbine-length one really desirable for reasons of felt recoil and reliability?

I'm getting more and more into AR's and want to put together what I want rather than standard factory offerings and am curious about this. I've had a 24"-barreled AR with a rifle-length gas system but can't recall it feeling a lot different. While I've put thousands of rounds through various AR's, I find my knowledge of their actual operation and details of variations somewhat limited as I begin muddling through to find out exactly what I want to build. Any help would be appreciated.

(I know that I can get lots of information on an AR-specific forum but wading through the search function there isn't as good as having my own thread HERE where I know that there are plenty of knowledgeable folks, too.)

 

[Onmilo]

I have not noticed any real discernable difference between the recoil or muzzle rise of a carbine length gas system over a full length rifle gas system.

If you aren't shooting full auto there is no real discernable wear difference on parts that I have ever noticed either.

A longer gas system offers a longer sight radius for iron sights.

If you are using magnifying optics the added advantage to a longer barrel and gas system is slightly higher velocity, less bullet drop, and less wind drift because of the higher velocity the bullet is traveling at ranges past 200 meters.
You will probably not notice these advantages with iron sights unless your eyesight is exceptional.

 

[Southern Raider]

A longer gas system taps into the barrel at a point where the gas pressure is lower, which tends to cycle the action less vigorously. While this may translate into a lower perceived recoil, it is probably up to the individual shooter.

However, shorter gas systems tend to be less reliable, but not necessarily unreliable. Faster carrier speeds put more demands on the extractor and tend to want to cycle at an earlier point in the cycle where the chamber pressure is higher. In other words, it won't cause the rifle to malfunction, but it does put extra demands on the rifle components that wouldn't normally be there.

For the record, all my ARs are 16" or less.

 

[taliv]

granted, it's subjective, but i think i can tell a difference

 

[Bartholomew Roberts]

This thread is good reading and will help you understand the differences in the AR gas systems

 

[taliv]

did you mean to post a link there, Bart?

 

[Howard Roark]

My experience is with servce and match rifles. Longer gas tubes are for heavy loads with heavy bullets. For reliability.

Sometimes there is a problem with overpressure and dwell time shooting the standard length gas tube with a barrel over 24". With the standard length tube the bolt is trying to unlock and extract before the chamber pressure has dropped. A longer tube lets the bullet be farther down the barrel and makes the gas travel farther for lower pressure. Another problem is bolt override. Shooting heavy bullets fast can make the bolt cycle so fast it overrides the next round in the mag. Tearing up the rim as well.

There are tubes that are 2" longer than the standard length for this. Lower pressure, longer dewll time.

I have two 26" barrels that have the standard length tube and shot them with no problem. The trick is to properly size the barrel port. Most people make the port too big. This assures cycling with lighter bullets and causes problems with the heavy ones. I find that a .090 port works well.

A properly tuned AR should eject the casings perpindicular to the rifle. If it slings them forward then there is too much pressure on the bolt/carrier. This can be fixed by moving the gas block to partially cover the port.

I hope this helps.

 

[Bartholomew Roberts]

I did mean to post a link there. Here is the thread:

http://www.thehighroad.org/showthread.php?t=199626

 

[strat81]

I've shot a few different ARs and I'm not sure how much of the felt recoil can be attributed to:
-Ammo
-Stock
-Heavier gun (20" HBAR vs. 16" M4 profile)

On a 16" CAR gas gun, you can change the buffer to a heavier one to help mitigate some of the felt recoil. However, .223 recoil is a joke. As for the wear and tear on the gun, a few credible sources says it can hurt the gun. How much? Who knows. Plenty of CAR guns out there with high miles that are running fine.

Buy what you like.

 

[Bartholomew Roberts]

Keep in mind that we aren't talking about a dramatic difference in felt recoil (though most people notice a difference). There just isn't that much recoil in a .223 to begin with.

The big place the smoother feel of the longer gas systems come into play is rapid fire with magnified optics or shooting on the move (i.e. 3-gun).

Nicely tuned gas system + decent brake + good stance + .223 = a dot that just hovers right on target without moving during shooting. Less recoil than some video games.

 

[DnPRK]

The big contributors to felt recoil is the weight of the rifle and weight of the bullet (the "M"s in the momentum equation). A heavier rifle (24" barrel) and lighter bullet will provide a marked decrease in felt recoil.