AR-15 Gas Piston System

[RhinoDefense]

The action will stay a lot cleaner and quite a bit cooler.

No. The difference in cleanliness is minimal and the temperature difference between the "DI" and "GP" systems is about 40 degrees.

Here's some reading the OP should do. What many people fail to realize is the AR15 operating system does use a piston and is NOT a direct impingement gas system, as stated in Stoner's patent documents.

http://www.m4carbine.net/showthread.php?t=99050

and Steve from ADCO here:

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

 

[MCMXI]

just don't try to pass off the current generations of miracle coatings and piston retro-fits as being elegant solutions to that problem.

Since I stated in my post ...

"The current attempts at solving this issue may not be the most elegant but engineering always has been and always will be an iterative process."

... clearly I'm not.

No. The difference in cleanliness is minimal

I own and shoot both GP and DGI ARs the difference in cleanliness in the BCG is significant and I use lubrication in my POFs since I'm not in the desert. I've never taken temperature readings of the BCGs but after running through three 30-round magazines in a couple of minutes I was able to remove the BCG from my P415 and hold it in my hand ... it was barely warm let alone hot.

 

[JustinJ]

No. The difference in cleanliness is minimal and the temperature difference between the "DI" and "GP" systems is about 40 degrees.

Celsius or Fahrenheit? How many rounds and how much time between shots? Gas system length?

Here's some reading the OP should do. What many people fail to realize is the AR15 operating system does use a piston and is NOT a direct impingement gas system, as stated in Stoner's patent documents.

Its matter of semantics. Wether or not you call them "op rod" ARs or "piston" we all know what we're talking about. Just because you want to call DI ARs piston driven doesn't change anything.

The arguement that pistons get dirty as DI bolt/carriers is true but the question is wether or not crud can impede function at said location and will the crud at the piston be removed as the gun cycles. Another possible variable with the DI is how external crud such as dirt and dust act when exposed to hot gasses inside the receiver as will not happen in a piston system.

 

[kfgk14]

If you want a piston AR as a novelty item and or a work of art I say damn the critics and just go for it! whichever one you choose will probably work fine.

However, if you are laboring under the mistaken belief that piston guns offer significant advantages over direct gas impingement ARs that are not offset by their own design limitations then i respectfully submit that you need to do more research.

Trust in this. Direct impingement is the better system. Mil-spec components and synthetic motor oil will do wonders where gas piston systems will wear, have proprietary parts, and not be made to any set standard.

 

[valnar]

Take a look at the PWS offerings if you want a piston. I eliminated the others after talking to some people who have used several brands. No...I don't own one, but it's on my short list of guns to buy.

I don't believe DI is better than Piston as every single DI fan on this board would be touting the benefits of pistons if history was reversed and Stoner designed the original AR15 to be that way instead. Then some people would come along saying they could improve it with their new fangled DI retrofitted Upper discombobulator and the naysayers would be out in full force. What the military blesses is not always the best available technology (Beretta 92FS?).

Like every design, both have their pros and cons.

 

[taliv]

yeah, actually, if the AR as a system was piston driven, with millions fielded through the last 60 years of conflicts, and it was working as well as DI has, sure, I'd be saying the same thing. there's always room for improvement, but i wouldn't spend an extra $300 to "upgrade" the piston to some fly-by-night company's DI that has produced a thousand units, 99% of which have had fewer than 100 rounds put through them from a bench, shooting groups.

 

[Bentley4700]

No. The difference in cleanliness is minimal .

This is just plain not true. My DI AR is dirtier after 20 rounds than my piston AR after 200 rounds of the exact same ammo. Piston AR's BCG's stay MUCH cleaner.

 

[MistWolf]

Wow. Lots of disinformation in this thread. Here we go with semantics again. No, we don't know what you're talking about. Eugene Stoner himself wrote in the original patent the system he designed is not a conventional direct impingement. Semantics? No.

When I perform a repair on the airliner you or your loved ones will ride in, should I rely on "semantics" to get the job done? Or do you want me to have an understanding of the tech data and what it really means?

Before arguing whether or not a design change should be made to an AR, one should have a good idea what the original design is, what is being changed and why.

You cannot add a piston to the original AR. Why? Because it already has one. Or do mean you want your AR to have a second piston? While "One is None and One Is Two" I don't think having a back up piston will work. Or perhaps you want a cascade system, where the first piston starts the process and the second one finishes it?

...right

Those who suggest converting the AR to a piston system don't know the AR already has a piston due to a lack of knowledge. We should listen to the advice of somebody who doesn't understand how the AR works and is supported by those who claim the difference is just a matter of semantics?

Come to think of it, I do know what you mean- that "you" are ignorant of the facts and do not care to learn. Perhaps "you" will see it another way and that's ok. It is, after all just a matter of semantics and well, you know what I mean

 

[Cesiumsponge]

Meh, this is why I rely on another unnamed forum for technical AR discussions. Let me know when the military selects a boutique piston retrofitted AR, pits it against the current workhorses in a side-by-side test and it outperforms it by a margin large enough to warrant canning all the issued DI gas systems.

 

[jon_in_wv]

Build whichever one you prefer. You will never get a consensus on this forum. Some AR guys would NEVER admit a gas piston is better than direct impingement. Personally, I think if you are looking for real reliability the AR isn't the first place I would look. So the DI is just fine for what it is and normally the GP is quite a bit more expensive. It's a great, accurate rifle and its fine like it is.

 

[SonOfRoost]

Thanks for all of the opinions, this just got muddled enough that I'm going to say that I'm perfectly capable of cleaning my rifle every week if I felt like it, even if I was in a warzone. and enough evidence tells me (as well as friends who have been to Iraq multiple times) that the direct impingement works as long as you can field strip your weapon occasionally. I'll be getting a DI, but not because of some opinionated nonsense from people that it was pointed out don't know all of the ins and outs of the original system, and therefore have limited scope on how another system works. Thank you for pointing that out MistWolf, but try to be a little more respectful to people who are misinformed next time, as a favor to any OP. This isn't meant to be a heated battle, I'm going to do DI because it's simpler, and proven, and if you ask me, if it's simple and it works, it's better than being complicated and working just as well. Thank you all.

 

[kozak6]

Let me know when the military selects a boutique piston retrofitted AR

The Marines are only buying about 4,476, so I don't know if they count. There's Delta Force, too.

Do the Norwegian Armed Forces count?

 

[XxBulletBendeRXx]

Well IF you fire 90 quick rounds out of a Adams Arms upper, Piston upper, you can pull the bolt carrier out and hold it with little no more the ambient temp. If you do the same 90 rounds in a DI Rifle, A Daniel Defense, same barrel length. The bolt carrier will likey be to hot to handle.
I know this cause I tested them both side by side on a 40 degree morning in climate conditions. (Not that you need to pull the bolt carrier out after 90 rounds at the range or wherever you may be using your rifle like that so it may seem irrelevent to many) SO..... If that makes one rifle better than the other from just that one difference, does that make one rifle design better than the other?
YOU CHOOSE?

 

[MistWolf]

...Thank you for pointing that out MistWolf, but try to be a little more respectful to people who are misinformed next time, as a favor to any OP...

Meant no disrespect towards you. You had a legitimate question and were looking for answers. If it came across that my sarcasm was targeted at you, I apologize and assure you, it was not. My bone of contention is with folks, upon being presented with the facts, immediately dismissed them.

I wish you the best of luck with your AR build. I found the experience of building mine enjoyable. While it's very simple to do, pay close attention to the details. For example, when performing the final torque on the barrel nut, it must line up so the gas tube fits inside the upper freely. It must float. If the barrel nut is off slightly, do not get lazy and try to adjust it "just a little" while the gas tube is in place. I uh, had a second cousin- yeah, it was my second cousin George- who tried such a short cut with near disastrous results. I'm lucky- er, my second cousin George was lucky the tube was only slightly bent and was easy to straighten out. Also remember, the only threads that get thread locker are on the gas key bolts

 

[buttrap]

I would have a opinion here but I aint going there.

 

[crossrhodes]

Whipping a dead horse

All I can say is that each system has it's pros & cons and it turns into the Chevy vs Ford argument. The DI has served us well, H&K has a proven system too (416) but the DI is not as evil as some portray, just check out BCM's Filthy 14 experiment. When the DOD makes its final decision on a piston system then that's the one I will go with simply because of the compatibility and availability of parts for us recreational shooters. My personal opinion is LWRC makes the best piston system going.

 

[Tirod]

What seems to confuse the issue is that the claim of cleanliness isn't unfounded - it's misdirected.

Sure, a piston Bolt Carrier Group is cleaner - it doesn't have gas directed into it.

I will contend that piston to piston, it aint. Compare the piston face of the DI bolt to the piston face from the cylinder on the barrel. Equally dirty.

Since they are getting gas residue on them, is it really that good an idea to then regard maintenance as no longer needed? Do you now have a reason to neglect it?

All the argument about which is cleaner where, and what does the Army insist on? Clean and inspect it daily, no matter what. Why? Because gas residue isn't the problem, it's environmental contamination. Either system will tolerate shooting 6-10 full combat loads in them during the day, if the soldier can survive that intense a situation. It's the mud, debris, vegetation, and body parts that will stop it.

Buy an AR and put the piston wherever, please don't justify doing so to excuse neglect and poor maintenance, and then blame design.

Piston to piston, they get equally dirty. The ammo dumps the same amount of residue regardless.

 

[Cesiumsponge]

The Marines are only buying about 4,476, so I don't know if they count. There's Delta Force, too.

Do the Norwegian Armed Forces count?

A link to article(s) that substantiate your claim?

Edit: I assume you mean the HK 416 and M27 IAR?

 

[JustinJ]

Before arguing whether or not a design change should be made to an AR, one should have a good idea what the original design is, what is being changed and why.

Saying the AR is a piston system already does nothing to address the reasons why people are advocating a change to the system. Sorry, but trying to win an arguement by definition is a dodge to the topic at hand and a pretty lame debate tactic. Most people consider a piston to be a seperate rod or disc that imparts force on another mechanical device to cause it to move. The confusion comes from the fact that they are not usually one in the same. You can call it a piston, rod or just long narrow piece of metal but the point is still to reduce the amount of burnt carbon that is introduced into the receiver. Knowing the technical definition of a piston is not needed to see a benefit to reducing hot gasses and burnt powder inside the receiver of a gun. Nor is it needed to understand how any AR works. I sort of doubt anybody here was not aware that the returning gasses from the gas tube are what drives the bolt and carrier. Arguing that the hot gasses and burnt powder are not a problem or not a big enough problem to justify the weight or potential malfunciton of an op is actually germane to the topic at hand.

The term "direct impingment" refers to the fact that the gas acts directly on the carrier as opposed to most other designs in which the gas acts on a rod which acts on the carrier.

You cannot add a piston to the original AR. Why? Because it already has one. Or do mean you want your AR to have a second piston? While "One is None and One Is Two" I don't think having a back up piston will work. Or perhaps you want a cascade system, where the first piston starts the process and the second one finishes it?

Speaking of being "ignorant of facts"...if you want to get technical you can't add a second one. You can only reconfigure the system so that the carrier is no longer acting as the piston. If you add a piston above barrel there will no longer be a fluid acting on the carrier so it can no longer be considered a piston.

...right

 

[jon_in_wv]

It never fails that a piston vs DI, AR vs AK, Glock vs XX, always boils down to name calling and nonsense.

 

[Robert]

Pistons are a solution looking for a problem. I clean my AR every few thousand rounds, even then it is not a hard process, and keep on rocking. If you want a pistol kit or upper get one. It is your money, not mine. If it were my money I'd buy more ammo...

 

[JustinJ]

In regards to the DI AR being piston driven already it also depends on which dictionary you read, as in semantics:

Merriam Webster: a sliding piece moved by or moving against fluid pressure which usually consists of a short cylindrical body fitting within a cylindrical chamber or vessel along which it moves back and forth

The Free Dictionary: A solid cylinder or disk that fits snugly into a larger cylinder and moves under fluid pressure, as in a reciprocating engine, or displaces or compresses fluids, as in pumps and compressors.

By the first definition one could call a DI AR piston driven but by the second definition an AR carrier/bolt can not be a piston as neither are solid...semantics.

 

[justice06rr]

I think it's really funny how the DI people get all worked up to convince everyone within shouting range that "DI Good," "Piston BAD." In fact, Armalite worked on an "upgrade" to the original AR design - the AR18 - a short stroke piston powered rifle.

SIG makes piston rifles, FN makes piston rifles, HK makes piston rifles, the M1 is a piston rifle, the M14 is a piston rifle - I think piston rifles have been proven to work.

The idea that there's more parts to break is like arguing that you should only buy 4 cylinder automobiles because cars with more cylinders have more parts to break. There is NO proof that anyone can give in piston rifle longevity other than anecodatal stories which don't count as real data.

I own BOTH types of rifles and can only say they're different, and one is not "better" than the other despite all of the protestations and "proofs" given by the DI disciples.

Whether they'll admit it or not, the piston does run cleaner - a lot cleaner. If that's important or not is up to you and not someone else quoting "statistics" about running xxx,xxx,xxx,xxx number of rounds through their rifle with "no problem." Or, a friend of a friend's first cousin's best friend's uncle who said he heard about a guy who went to a carbine class and met someone who had run yadda....yadddaaaa...yadddaaaa....

Here's what I know from owning two different types of guns.

1. Weight: My piston gun IS slightly heavier than my DI - by 6 oz. The weight difference is dependent on how you have the gun configured as well. Top rail only, full length quad-rail system, type of stock, barrel profile, etc. The point is - there's more to weight than "Piston Heavier."

Given each gun being configured exactly the same - a piston system will be marginally heavier. If carrying six ounces more is a big deal - as we say in bicycling, "Want to eliminate 6 ounces from your bike?" "Lose weight."

2. Carrier tilt: in a well designed piston rifle, carrier tilt is a non-issue. This includes AR style rifles. The Barrett REC 7 does NOT have carrier tilt because the bolt + carrier are designed to eliminate it.

3. Proprietary parts: YES, piston systems have proprietary parts. The idea that "I can interchange parts in my rifle with any other DI" is nice, but, is it necessary? That's something only you can answer. I can easily interchange parts in Glocks and even 1911's - but, I've never done it, never had to do it, and never wanted to do it. So, I'm not sure what type of point this is making.

If you're into building rifles (and I'm not) - that may be a germaine to the discussion, othewise it's just another specious talking point masquerading as "important data."

In a way, that's like saying "I'm never buying and FN SCAR because you can't interchange parts with an AR, HK, or SIG." Whatever. If parts interchange is a make or break buying point for you fine - it's not for me.

I'm probably NEVER going to shoot a rifle enough to break anything on a quality product anyway.

4. Your Quad Rail: now there's a real problem overlooked by the DI proponents as they hop up and down attempting to stomp piston rifles into a goo spot. Your quad rail will probably not fit on a piston upper, so you might want to check that prior to buying any type of piston conversion system or piston upper. I know on the REC 7, the only quad rail system that fits is the Daniel Defense Omega X-Rail specifically made for a piston rifle.

If using your quad rail is important, buy a DI, you can expect it to fit that.

There, now all of the DI aficiandos should feel better because, in the end, I had to cave in and recommend a DI upper. Yes, I did, but not for any of the "reasons" given previously, only on a pragmatic choice basis of matching what is already owned - the quad rail.

Some good points, but the DI people are not getting worked up by any means.

They're just saying that the DI system has worked for decades and there isn't any real advantage to Piston other than running cleaner.

IMO it's more like the gas engine vs electric cars. We all know gas motors have worked for decades, but also produces more emmisions compared to the cleaner electric cars.

Flip side to that is batteries are expensive to make and replace -- and still bad for the environment come time to dispose. And they are more expensive, just like Piston AR's.

 

[MistWolf]

Speaking of being "ignorant of facts"...if you want to get technical you can't add a second one (ed.- piston). You can only reconfigure the system so that the carrier is no longer acting as the piston. If you add a piston above barrel there will no longer be a fluid acting on the carrier so it can no longer be considered a piston.

...right

That is the point I was making. The AR already has a piston

FACT:
1) The AR has a piston. It is part of and in centerline with the bolt to eliminate offset recoil to reduce muzzle climb.
2) The AR has a cylinder which is part of the carrier.
3) The AR does not have an actuator rod.
4) Eugene Stoner wrote in the original patent that his system uses an expansion chamber and is not a conventional direct impingement system.

Here is the link to the patent. You may research it for yourself- http://www.google.com/patents?id=ETJjAAAAEBAJ&printsec=abstract&zoom=4#v=onepage&q&f=false

 

[MistWolf]

In regards to the DI AR being piston driven already it also depends on which dictionary you read, as in semantics:

Merriam Webster: a sliding piece moved by or moving against fluid pressure which usually consists of a short cylindrical body fitting within a cylindrical chamber or vessel along which it moves back and forth

The Free Dictionary: A solid cylinder or disk that fits snugly into a larger cylinder and moves under fluid pressure, as in a reciprocating engine, or displaces or compresses fluids, as in pumps and compressors.

By the first definition one could call a DI AR piston driven but by the second definition an AR carrier/bolt can not be a piston as neither are solid...semantics.

You correct that a true DI system does have a piston which is part of the carrier. The piston fits into a cup at the end of the gas tube, which functions as the cylinder. Here is a diagram of the Ljungman DI system
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