Hey, I've always wondered. What function does the gas tube serve? Do all rifles have gas tubes?

Thanks for answering my rookie question!

In the Ar15/M16 series of rifles, the gas tube makes the bolt, bolt carrier, upper receiver, chamber, trigger group and lower receiver filthy.

It's supposed to tap off some of the gases pushing the projectile out of the barrel and cycle the action. It does this but by allowing the gases back into the receiver group it makes things really funky really quickly. Gas pistons are a much better design in terms of maintaining reliability between cleanings.

In an AR-pattern rifle, there is a gas port (hole) in the top of the barrel underneath the front sight base (or gas block on rifles w/o front sights) and a matching hole in the base itself. The gas tube fits into the rear of the front sight base and runs along the top of the barrel back into the upper receiver.

Inside the receiver, the rear of the gas tube plugs into carrier key (the piece sticking up above the front of the bolt carrier) which is hollow. The carrier key has a hole in the bottom of it that leads into a chamber in the bolt carrier that is created when the bolt collapses into the carrier as it turns and locks into the barrel extension.

When a round is fired, the projectile passes the gas port and the pressurized gas behind the projectile vents into the port, through the sight base, into the gas tube, back to the carrier key and into the carrier/bolt chamber. In the chamber, the gas pressure pushes the carrier back...because that is the only way it can 'give'...with enough force to cycle the the action.

...and Sukebe is exactly right...which is a big reason why the gas tube is pretty much unique to the AR-pattern rifles.

So if my gas tube(or any of the gas system parts) fails, I basically have a bolt action ar15?

Yep (well I guess it depends how bad the system fails).. You can actually get gas blocks with valves in them so you can switch them off and accomplish the same thing...

Yes, but that is true of ANY gas system-type...when parts fail, they don't function.

One of the advantages of being an issue weapon with a major military power is that weapons get constant use and evaluation. Just through attrition (of equipment AND people), unsatisfactory designs and sub-standard parts get tossed as designs are refined and part-quality improves. By that process, the current AR-pattern 5.56mm rifles (from quality manufacturers) are reliable and safe in function.

The biggest issue with the AR-pattern gas system is that is just moves the gas so damned far using what it probably one of the most fragile function-critical parts of a current-issue combat weapon...that damned gas tube!

The tubes rarely fail in/from use (from my experience), but they are exceptionally fragile and can be damaged if the rifle falls from a not-to-high location, in the right orientation, onto a hard surface...and they can be easily damaged by hand, too (unintentionally or intentionally).

Examples I have seen:

M-16 falling off of a stairwell landing and hitting the middle of the top handguard on a  handrail below when the soldier was wounded in the hand and dropped his rifle.

A heavy-barrel AR-15 upper being cleaned w/handguards off and the owner picking the upper off a table by the barrel and losing his grip. As he reached for the falling upper, he caught it by the gas tube which pulled out of the upper receiver as it folded then snapped off at the front sight base.

Injury and inattentiveness aside, damage like that shouldn't really even be possible in a military weapon...I mean, come-on, you can put an M-16 out of commission with your bare hands for Christ's sake!!!...but I can't argue with the success and lifespan of the design.

Wow I didn't realize how fragile it was.

Wanna see nostalgia?


Go see one of the original video presentations for the AR15/M16s.

[url]http://66.155.8.108/streaming/streamingMain.htm[/url]

Click on one of the links under "Rifle, XM16EL Operation and Cycling"

And Swedish AG42s, and Egyptian Hakims, and French M49s and 49/56s, and Danish Ljungmans, and-------[:D]

For Mr Troy (staff):

The diagram that you posted is by far the best diagram that I've ever seen of the operation of the AR15.  Postings such as that are one of the big reasons why I like this website so much.  

No way that I can print that thing; is there any way that I can optain a hard copy of it and of any others (that are in the series, if any)?

Thanks again for posting that illustration.

Mike Sigman
[email protected]

mbsigman,  Check your E-mail.

DILBERT_556

Less weight, and less reciprocating mass too.

My favorite image...

[img]http://home.bak.rr.com/varmintcong/misc/xray.jpg[/img]

Simply right click on the picture and chose "Save Picture As".  Now it is a GIF file whereever you saved it to.

You can print it with whatever picture viewing program you use on your computer, ACDSee, Irfanview, etc.