Gas tube; how does it work?
Newby AR15 owner question. Which way does the air travel in the gas tube and where does it go? I'm assuming it passes thru the bolt carrier key and into the tube, along the length of the barrel, thru the front sight post, then where? Right back into the receiver??? Is that why this rifle gets so damn dirty? Does the gas exit the rifle somewhere and if so, why not thru a hole in the front sight post since this is where the tube runs to.
Also, I see that Fulton Armory sells adjustable gas tubes. Any benefit to these for anything other than DCM?
The gas runs back into the bolt carrier and into the expansion chamber created by the bolt and bolt carrier. The gas forces the two apart, moving the bolt carrier to the rear and unlocking the bolt, until bolt (acting as the piston) moves far enough that the gas escapes from holes in the bolt carrier and out the ejection port.
Its the reverse of what you said, starts at the sight and come out those little holes in the side of the bolt carrier.
You've got it backwards. The gas pressure behind the bullet vents into the gas port (in the front sight post), through the gas tube, and back into the carrier key which provides the force to push the bolt and carrier rearward. This, in turn brings about the whole extraction & ejection sequence, along with compressing the buffer spring which provides the force for the bolt & carrier to slam home (and thus load a fresh round). So the reason the gun gets so dirty is that you're blowing hot & dirty gasses back through the gas tube and into the bolt and receiver.
To add: Once the gas reaches the chamber in the carrier where the bolt rings seal, the gas pressure causes the bolt and carrier to try to seperate, causing the carrier to begin to move rearward. Once it's moving the carrier continues moving due to inertia until the recoil spring overcomes the inertial force of the carrier. The bolt unlocks due to the shape of the groove in the carrier the cam pin rides in.
So there is a hole inside the barrel. I was suspecting that. Thanks guys; great info.