Eugene Stoner AR Operating System is not a conventional impinging gas system

[Medic!]

There are three different types of operating systems being discussed here:

1. The firearms you mentioned above are Op-rod driven guns (which can be broken down into floating interrupted, or direct attach pistons)

2. Direct Impingement guns, would be like the MAS-49 and Ljungman Ag m/42

3. Internal Expansion System (Stoner)

This is why one shouldn't refer to the op rod driven guns as piston guns, even though they all have pistons. Simply ID'ing them as piston operated isn't detailed enough to understand the method of operation.

If you want to use the word "direct" for the Stoner system, then it would be appropriate to call it a Direct Internal Expansion System, not Direct Impingement. You would also call the AK a Direct Gas Piston system.

I like direct internal expansion.

But that sounds a little misleading also?
The gas is not expanding in the bolt/carrier group.
It's expanding from the burning powder in the barrel. And being pushed to the carrier group through the gas tube.
Although it may not be technically a gas impingement design.
The gas dose impinge directly on the carrier group.

In an AR the gas from the gas tube goes into the space between the bolt and carrier and this forces the two away from each other.
The bolt can't move forward. So the carrier moves back. As it dose this. It cams the bolt to the unlocked position.

The energy of the expanding gas imparted to the mass of the carrier.
Causes it to carry the now unlocked bolt rearward.
This rearward motion is also helped buy the residual pressure in the barrel acting on the brass and [now unlocked]bolt face.

At least that's how I see it. But I'm Lisdexic.
I know how it works. But have no Idea what it's really called?

On a side note.
The energy exerted on a standard AR bolt. Occurs in the center of the carrier group. As the carrier and bolt are forced away from each other buy the gas between.
In line with the barrel/buffer tube.

With a piston AR. The energy is imparted to the top of the carrier.
This causes a tilting action.

I know it works. But I don't like that.

The Aluminum receiver was designed for straight line rearward movement of the carrier/bolt group.

 

[madcratebuilder]

I hear you there, I usually don't either but grinds on me from time to time (sort of like the clip vs. mag thing) and I slipped. Oh well, hopefully it will educated.

I'm glad you posted this, I wanted too but was lazy. After twenty years of seeing the same posts I don't care anymore. That song well float around in my head for a few hours now.

 

[Boboclown]

With a piston AR. The energy is imparted to the top of the carrier.
This causes a tilting action.

I know it works. But I don't like that.

The Aluminum receiver was designed for straight line rearward movement of the carrier/bolt group.

Different manufacturers have a way around this. Some use rails, most just use an anti-tilt buffer. More "meat" in the back of the bcg helps somewhat. One went with a long-stroke piston and enhanced buffer tube. Supposedly a long stroke piston helps but I'm not an engineer so I say supposedly.

Granted, I generally stick with the standard AR-15s... With the big brother .308 I don't care due to lack of standardization anyways.

 

[Ownerus]

titzonritz is indeed correct on this. Unlike the "direct impingement" MAS49, the AG42, the Rashid and Hakim, the standard AR is an unconventional coaxial gas piston. The bolt is the stationary piston and the bolt carrier is the moving cylinder. The gas tube is just a really long gas port in the barrel. Sorta like the SVT-40 and Mini 14 except for the length of the gas port. Stationary piston, moving cylinder with a longer non-coaxial bolt carrier (op rod) to make up for the short length barrel port. In my view, the real difference in these is the length of the gas port/ distance between the hole in the barrel and the actual moving parts. Direct impingement is a term of convenience but not very accurate when used with the AR system. As someone said, they're all gas operated (even the "recoil operated" guns), it's just in trying to explain the execution of the details we run into the weeds. A fun topic though and helpful to understanding