AR- Piston or Direct Impingement?

[danco]

I've always thought the name "Direct Impingement" was unfortunate. A more descriptive name would contain the word "coaxial" as this is the feature that truly distinguishes this system from all the others. Perhaps "coaxial piston" or "coaxial system" or some such. It is indeed true that all ARs, indeed, all centerfire auto rifles except the handful of recoil operated systems, are piston systems.

Well, the term "coaxial" implies that the axes of two components (in this case the barrel and the piston) are parallel, but not necessarily that the axes are the same. I think a better description of the Stoner system is just "axial" or, even better, "in-line."

The actual patent is a great read. In the description, Mr. Stoner states: "This invention is a true expanding gas system instead of the conventional impinging gas system."

In light of this, I will never again refer to my 6920 as a direct-impingement weapon.

Great info, MistWolf! Thank you!

~Dan

[mikeshin1023]

Pretty sure "coaxial" means the same axis.

From Dictionary.com:

"Also, co·ax·al  [koh-ak-suhl] Show IPA. having a common axis or coincident axes."

[An Undocumented Worker]

Well, the term "coaxial" implies that the axes of two components (in this case the barrel and the piston) are parallel, but not necessarily that the axes are the same. I think a better description of the Stoner system is just "axial" or, even better, "in-line."

The actual patent is a great read. In the description, Mr. Stoner states: "This invention is a true expanding gas system instead of the conventional impinging gas system."

In light of this, I will never again refer to my 6920 as a direct-impingement weapon.

Great info, MistWolf! Thank you!

~Dan

coaxial [kəʊˈæksɪəl], coaxal [kəʊˈæksəl]
adj
1. (Mathematics) having or being mounted on a common axis
2. (Mathematics) Geometry (of a set of circles) having all the centres on a straight line
3. (Electronics) Electronics formed from, using, or connected to a coaxial cable

Pretty sure Coaxial is the correct term.

[danco]

Ok...but I still like the sound of "in-line piston system" better. Has a nice ring to it and sounds kind of poetic...

The salient point is that the Stoner system is not "direct impingement"...

~Dan

[MistWolf]

More precisely, it says "This invention is a true expanding gas system instead of the conventional impinging gas system."

It doesn't matter if the AR is a direct impingement system or not. The point being is it does have a piston (and I suppose push come to shove, so does the conventional DI system) and that the offset piston upper adds an actuator rod and introduces off center recoil.

Critics of the AR inline system talk about tight tolerances. Yet the carrier has little contact with the upper receiver. The tight tolerances are between the bolt and the carrier.

Perhaps someone with more experience with the AR can tell us where most of the crud and debris collects in the AR and what the direct effects are. I read statements that carbon build up on the tail cone of the piston doesn't matter. I can see where debris in the barrel extension would prevent the bolt from locking up properly. I also know that keeping the action lubed will keep it running.

The offset piston system can produce tough and reliable rifles. After the AR, Eugene Stoner went on to engineer other weapons using offset pistons. But his design that went on to be successful is the inline piston of the AR

[sinlessorrow]

The ar as we know it is also tough and reliable.

Also carbon buildup doesnt make a diff unless its in excess, like 5000 rounds. In the military you wont even come close to that before cleaning. A combat load is generally 7 magazines.

Wipin down the ar-15 once a day and lubin will keep it running

[MistWolf]

The ar as we know it is also tough and reliable...

I didn't mean to imply the AR isn't. I read reports from the first Gulf War that the AR proved to be the most reliable of the 5.56 NATO rifles that saw action. One advantage the AR has is that it's spent more time in the crucible of combat in the harshest of conditions than almost any other rifle

[Arctic1]

Also carbon buildup doesnt make a diff unless its in excess, like 5000 rounds. In the military you wont even come close to that before cleaning. A combat load is generally 7 magazines.

Carbon buildup is not the only issue for mil guys.

Sand from weapons being exposed to the elements, dirt and vegetation getting into the action or getting on the mags in the pouches. Snow and ice getting into the action.

I had a guy whose weapon malfunctioned during a live fire ex, squad hasty attack. Bolt wouldn't cycle, and we couldn't lock the bolt to the rear. It was stuck, barely out of battery. With a leatherman and some brute force, we finally managed to get the bolt free.

Upon inspection of the barrel extension and inside the reciver, we saw small pebbles, the size of coarsly grated pepper. They locked the action up.

During one operation a team had several guns fail to function after a while, during contact; HK416's, MG-3's and M2 .50 cals due to mud and dirt getting EVERYWHERE.

Lubing helps, but only to a certain point.

[sinlessorrow]

Carbon buildup is not the only issue for mil guys.

Sand from weapons being exposed to the elements, dirt and vegetation getting into the action or getting on the mags in the pouches. Snow and ice getting into the action.

I had a guy whose weapon malfunctioned during a live fire ex, squad hasty attack. Bolt wouldn't cycle, and we couldn't lock the bolt to the rear. It was stuck, barely out of battery. With a leatherman and some brute force, we finally managed to get the bolt free.

Upon inspection of the barrel extension and inside the reciver, we saw small pebbles, the size of coarsly grated pepper. They locked the action up.

During one operation a team had several guns fail to function after a while, during contact; HK416's, MG-3's and M2 .50 cals due to mud and dirt getting EVERYWHERE.

Lubing helps, but only to a certain point.

Certainly there are other things, i was just stating the carbon buildup from the stoner system is a non issue.

People make it out likes its a plague that kills the rifle but its not an issue if its cleanedduring downtime.


Eta: my comment was not aimed at anyone just a general comment

[Koshinn]

Why do most modern assault rifles utilize short stroke (op rod) or long stroke (AK style) rather than the Stoner type piston?

Actually, do any new weapons not of the Ar 15 fow utilize it? Might there be a reason for this? I'm just asking as I don't know.