I’ve been reading this forum, along with other AR forums, for quite some time.
I find it amusing that most of the readership here and on the other forum really doesn’t understand how Gene Stoner’s brilliant design works. Now, I don’t know where all this “direct impingement vs. gas piston” discussion all started. And I’m not sure that I even know what direct impingement means. However, the AR is a piston design in the same sense that the M1 carbine is a short stroke gas piston design. Let me explain. When the cartridge ignites gas is blown back down the gas tube and down the gas carrier key into the gas piston chamber. This chamber is a cylinder inside the bolt carrier. It is blocked at one end by the 3 gas rings at the front and blocked at the rear end by the piston disk located on the firing pin. The FIRING PIN is the PISTON . When gas expands in this chamber it expands equally in all directions. With this expansion the bolt goes FORWARD, moving further into the chamber. This takes the strain off the locking lugs so they don’t grind past each other when they unlock. At the other end of the chamber, the disk on the end of the firing pin short strokes back, strikes the cotter pin, which takes the full brunt of the force and forces the bolt carrier to the rear. As the bolt carrier moves a short distance to the rear, the bolt is still pushed forward at this point, the key moves in the cam and the bolt unlocks. As the bolt carrier moves to the rear, while the bolt is unlocking the exhaust holes in the carrier clear the gas rings and the excess gas is exhausted out the two holes that you see in the carrier through the ejection port. The beauty of this design is that all reciprocating motion is ON AXIS to the BORE. This is an important part of the design. It reduces wear and tear, reduces the felt recoil impulse and muzzle flip.
Now what everyone is calling a piston design is in reality a piston dislocation off-axis. You’re just moving the piston from it’s location behind and axial to the bolt to a location above the barrel and off-axis. This is not the way the gun was designed to work. By striking the carrier off axis with a rod, a la AK-47, you tilt the bolt carrier in the receiver. It was not designed to move in this way.
All this does is increase wear and tear, steel against aluminum. You’ve also removed the gas rings that cause the bolt to move forward at the time that it’s trying to unlock itself from the barrel extension. This puts undue strain on the locking lugs. When the piston rod strikes the bolt carrier the bolt is no longer pushed forward and forced to grind past the locking lugs as it gets dirtier with every shot fired.
The major problem here is that everyone wants to make something out of Stoner’s design that it was never intended to be. Stoner’s design is brilliant from an engineering stand point. Folks, if you want a “piston driven” AR, you already own one. If you want a rifle with the piston off axis to the bore buy one that was designed from the start to function in that manner. The AR wasn’t design to function efficiently any other way. All moving the piston does is create it’s own set of problem by increasing wear and tear in the receiver and the locking lugs.
As an aside, I would not lube the rear portion of the bolt behind the gas rings. Yes, the gun is over gassed and, yes, it will work with only one gas ring. The gas chamber doesn’t need to be “gas tight”, so to speak, in order to function. It’s not recommended to oil the piston chamber of any semi-auto.
Enough said. Enjoy your ARs
