Thread: purpose of the gas rings?

Retrieved: December 08, 2013

I've been reading about the gas rings on the bolt. There are three, and a spec for orienting them properly on assembly, but from the pictures I've looked at (I don't have an AR), they don't seem to have anything to do with the gas system. The gas key is up top and forward, and any pressure the rings might handle should blow out the ejection port, from what I can tell.

There are lots of pages about the evils of worn or broken gas rings, but after a couple of hours of searching, I still don't know what they're supposed to do...

Apparently I've made an invalid assumption somewhere along the way. Can someone straighten me out here?

moleman
12-06-2010

The expansion chamber on an ar15 ect is between the back of the carrier bolt hole and the back side of those gas rings. The gas presses on those and the carrier and since the bolt can't go forward the carrier is pushed back to turn and unlock the bolt.

[486]
12-06-2010

The top drawing explains the internal piston system of the standard "DI" AR.

moleman
12-06-2010

Thats a great explanation of it [486]. The back tail of the bolt is a tight fit to the bolt carrier, is a smaller diameter and has a longer contact area so the gas loss isn't as great as it is from the front.

TRX
12-06-2010

Aaah! I didn't realize the gas key was hollow.

So the AR uses the gas pressure between the bolt and carrier to reduce friction from the multiple locking lucks as the bolt unlocks.

By the way, the coiled, one-piece gas rings some vendors are selling are known in as "Spirolox", and most of them seem to be used for holding wristpins in car engines.

[486]
12-07-2010

Originally Posted by TRX
So the AR uses the gas pressure between the bolt and carrier to reduce friction from the multiple locking lucks as the bolt unlocks.

That was just an old pic of one of my many arguments against piston conversion ARs.