AR- Piston or Direct Impingement?

[MistWolf]

The question still comes up and the debate rages on- “Should I Get a Piston for my AR or Direct Impingement?” The answer is, the AR already has a piston and none use a direct impingement system.

First, let's take a look at a conventional Direct Impingement system. The key feature is that gases act directly on carrier. The gas travels through a gas tube to act directly on the carrier. The following diagrams show the DI system of the Ljungman Ag m/42.



Eugene Stoner said in the original patent for his gas sytem “This invention is a true expanding gas system instead of the conventional impinging gas system.” The gases enter the expansion chamber inside the bolt carrier and drives the carrier rearward. The piston is actually the tail piece of the bolt. The rearward motion continues, unlocking the bolt and extracting the spent case.

The system is designed to be self regulating. When enough pressure enters to operate the action and the carrier begins to move, the key separates from the tube and cuts off the gas flow to the carrier. There are also vents in the carrier to allow the gases to escape and the pressure to drop inside the cylinder when the piston seals move past them. After that, the action is powered by momentum and returned into position by the energy stored in the action spring.

In the AR system, Eugene Stoner eliminated the actuator rod of other piston gas systems and incorporates the piston with the bolt and the cylinder with the bolt carrier to “...provide smoother operation and longer life of the working parts...” The patent goes on to explain that since all the actuating force is inline with the bore and bolt to the shooter's shoulder “all of the off center loads found in most other types of gas actuated weapons are eliminated” to cut down on “climb” during automatic fire.

The so-called “piston upper” (ie- Adams, HK416, LWRC etc.,) does not convert an AR from direct impingement system to a piston system. It converts the AR from an inline piston system to an offset piston system and adds an actuator rod.

Anyone tells you your AR needs a piston to run cleaner/cooler/tacticooler, tell them

"No thank you. My AR already has a piston"

Stoner Patent #2,951,424: http://www.google.com/patents?id=ETJ...page&q&f=false

Note: I will edit this post as my research continues, to correct any mistakes and for clarity

[sinlessorrow]

excellent write up

i gotta say stoner was a genius, its no wonder his system is still in use today as one of the best rifles in the world

[pilotguyo540]

Well said. I hope this gets stickied.

[N8rfastback]

Awesome explanation. That puts things into perspective.

Sent from my A500 using Tapatalk

[TacMedic556]

CAN WE GET A HALLELUJAH!

Right on. Excellent write up. Thanks.

[infidelprodigy]

Excellent explanation of the inner workings. Hard for detractors to argue with what Stoner wrote in the patent paperwork........

[J_Dub_503]

It's always nice to pick up more info on the firearm we love so much, great write-up. Strap up for all the naysayers' comments...they're sure to come.

[Suwannee Tim]

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.

[MegademiC]

Excelent post.

There was a post on TOS about this also, I believe by Steve from adco. (there are 2 "bigbore"s over there so im not sure which one wrote this). It has cut-section pictures to help people see what actually is going on.

http://www.ar15.com/content/page.html?id=535

Im assuming we can link there. If not, mods, just remove link and I'll pick up what you're throwing down.

[DeltaSierra]

Mistwolf -

Great post. Thanks for taking the time to write this up.....