TIL: the AR is not direct-impingement

[Boboclown]

By having the bolt carrier act as a movable cylinder and the bolt act as a stationary piston, the need for a conventional gas cylinder, piston and actuating rod assembly is eliminated.

The bolt is not the piston, it only acts as one.

The only thing one could really say is that the AR is not DI or piston operated. Just easier to call it DI.

 

[Vorpalis]

The bolt is not the piston, it only acts as one.

I don't mean this as insult, just an objective description: that statement doesn't make sense. Acting like a piston is essentially the definition of being a piston.

What distinction do you make between a piston and a non-piston that acts like piston? Can you provide evidence or a well-reasoned argument supporting your assertion?

 

[Boboclown]

I don't mean this as insult, just an objective description: that statement doesn't make sense. Acting like a piston is essentially the definition of being a piston.

What distinction do you make between a piston and a non-piston that acts like piston? Can you provide evidence or a well-reasoned argument supporting your assertion?

The AR is not a true DI gun, but its not a piston operated one either (excluding ones that include a short-stroke piston or long-stroke piston). The gas goes through the gas tube, and into the bolt carrier. Gas expands and pushes the bolt. The AR, if anything, would not be either DI or piston.

Its just easier to call it DI as its closer to a DI than a piston.

Again, even Eugene Stoner did not call it a piston operated gun.

 

[pigiron]

When you think about how it functions, the gas isn't directly pushing on the carrier

Except that it *is* directly pushing on the carrier. That's why the carrier moves!

 

[pigiron]

Gas expands and pushes the bolt.

No, it pushes the carrier. The bolt is initially mechanically locked.

 

[Boboclown]

Except that it *is* directly pushing on the carrier. That's why the carrier moves!

That's not how it happens. Gas enters the bolt carrier through the gas key, and the gas expands which pushes the bolt.
Its not a true DI, but its easier to say DI than "gas expansion system" all the time.

 

[pigiron]

That's not how it happens. Gas enters the bolt carrier through the gas key, and the gas expands which pushes the bolt.

That's not how it works.

The expanding gas simultaneously pushes against the bullet and the inside of the bolt carrier, the only parts that are not locked in place.

As the carrier initially moves to the rear the angled cam slot in which the cam pin rides causes the bolt to twist, unlocking the breech.

When the cam pin reaches the end of the slot the carrier continues its rearward motion finally pulling the bolt and the brass case to the rear via the cam pin.

 

[Boboclown]

The gas expands and pushes on the bolt, which causes the carrier to move, which in turn moves the bolt.

I didn't say the gas moves the bolt.

 

[pigiron]

The gas is pushing on every surface it reaches: the bullet, the inside of the barrel, the interior of the gas tube, the interior of the gas key, the inside of the brass case, the inside face of the primer, the bolt, the bolt gas rings, and most importantly the rear surface of the bolt carrier.

During the rearward movement of the bolt carrier, for the distance of the length of the cam slot, the carrier is moving to the rear and the bolt is only twisting.

 

[Vorpalis]

The MAS-49 is the clearest – and one of the only firearm – examples of direct impingement. Gas exits the gas tube (orange-ish brown) directly onto the face of the carrier (blue), imparting motion via the gas's inertia alone:


The important distinctions between direct impingement and a piston system are:

• One component resides inside another (not including the receiver);
• Together they form an enclosed space;
• When gas expands into this enclosed space, its pressure forces one of the two components to move relative to the other;
• Motion is imparted by the gas's pressure in the enclosed space, not by its inertia.

In the AR, these criteria are met by the bolt and bolt carrier. It actually doesn't matter that the cylinder moves while the piston remains still, because it still meets the above criteria. In order to argue the AR is not a piston system, you need to refute these points. Your repeated insistence that I'm wrong, no matter how adamantly you believe so, does not constitute a refutation or valid argument.

When @James Hedman described it as the gas "pushing" the carrier, this disregards the other half of the system – the equal and opposite reaction – that the gas is also pushing against the bolt and the interior walls of the cylinder (the carrier), so that's not a valid description. It's like pointing at a petal and claiming it's not a flower, while ignoring the flower the petal is a part of.

@Boboclown, you're right, semantically, that Stoner doesn't say "this is a gas piston", at least in the patent, but he does explicitly say that it's not an impingement system.

 

[pigiron]

When @James Hedman described it as the gas "pushing" the carrier, this disregards the other half of the system – the equal and opposite reaction – that the gas is also pushing against the bolt and the interior walls of the cylinder (the carrier), so that's not a valid description. It's like pointing at a petal and claiming it's not a flower, while ignoring the flower the petal is a part of.

You are right. But it really doesn't matter in which direction the gas is expanding as it is pushing in every direction. The enclosed space however goes all the way around to the inside of the cartridge case. The point is that the bolt carrier is the only part besides the bullet that can move and that is only towards the rear.

 

[Boboclown]

@Boboclown, you're right, semantically, that Stoner doesn't say "this is a gas piston", at least in the patent, but he does explicitly say that it's not an impingement system.

He also mentioned that the piston is eliminated from the gas system. To further that, he mentions it not being a conventional direct impingement system. That's different from saying it isn't a direct impingement system.