I have a Bushmaster about 15 years old. I converted to the Ares piston back in 2008. Would jam with steel ammo and would not run with some mags, especially 20
Round Pmags. I returned it to DI. Ate every thing I fed her with all different mags(GIs, Pmags, Cetme, a knock off 15 rd, and Thermold).
I must say I am happy again, but not about the $400 I spent for the kit.

I do have a Bushy M4 that is piston(Ares). It works great, but I only use brass ammo.  I have not run the steel ammo threw her.

Piston conversions are the answer to a question nobody asked,  but everyone thinks they need.

So true. The cleaning was much easier.

That is unfortunate you gave up with trying just one kit early in the game...

Hey OP, I don't care. Bye.

Did you convert to an ARES Defense manufactured kit or one that was produced by Bushmaster under our license agreement to them? There are differences but either way it is unfortunate that you had a problem with it. We stand behind everything that we make and we would be happy to discuss your experience and see if there's something that we can do to help. Please send an email detailing your experience to: [email protected]

I agree.

I like piston guns and the different designs intrigue me but my ARs are all DI.

DI just works.

LOL, many people have asked for a reliable AR that you do not have to keep wet and spend significant time cleaning. The above is a myth by DI loyalists. To each their own, while I enjoy my piston ARs...

Not everyone!
From a engineering standpoint I can see how a piston should run cleaner and cooler .
From  personal experience I know without a doubt that a standard AR , with a minimum of upkeep and lube , works just fine.

I don't much mess with full auto , cans, or pistols but the AR rifle or carbine is good to go in my book and I have no need to "fix" it


On the other hand if someone else has different wants, needs or uses and the piston helps them out I have no problems with that

You don't care, then you shouldn't have read my post.
BTW: Kindly go fornicate with a goat.

Some of the most successful weapon platforms past and present are piston based.
( Its not an accident ).

Direct gas works fine but piston guns run longer and cooler in the same firing conditions.
Buy or build what you like to use and enjoy.

Can you give some examples of these majority of successful firearms? Because from what I see the AK and AR-15 make up the majority of the world's small arms. With a large number of top countries Special Forces choosing the AR platform.

Examples:

M1 Garand
STG44
M249
M240
FAL
Any AK patern Rifle
G36
L86A1
AUG
Tavor
M14
Gas piston AR's
Galil
M1 Carbine

I can keep going as the list is far longer.

Compared to DI:

M16/M4/AR15
ENT 1901
Rossignol B2/B4/B5
MAS 40
Ag m/42

Interesting. So as long as it has a piston that makes it a successful firearm? The majority of that list has not seen any form of super wide adoption aside from the AK and the M249/M240 which I don't count when comparing to a individual rifle.

You even have guns like the M1/M14, G36, and the L85 which have all shown to be less than ideal guns that perform worse than guns like the AK. You cannot honestly believe they are a top quality gun.

When it comes right down to it, the AK and AR make up the majority of the world's individual rifles.

A piston gun killed Bin Laden

Everyone knows Obama killed Bin Laden.

And I'm sure he would have apologized for it if he had the chance.

I was just listing piston rifles. I'm not going to argue with you as science and engineers are the ones I listen to. Not people on the internet with an opinion.

How's this, from a mechanical engineer:
The AR15 was designed as a DI rifle for bolt thrust axial to the bore, creating very little contact force on the aluminum bearing surfaces of the upper.
Piston conversions on AR15's deliver off-axis forces into the carrier and bolt without the advantage of a forward guide rod fixed to the carrier for more positive alignment, which can lead to things like uneven wear.
This can be mitigated with changes to things like the carrier and buffer tube, but it is still a factor.

The ADCOR BEAR has guides built into the upper in order to stabalize the force. Also eplain PWS then.

OK, I'll take a crack at it: The AR15/M16 and the AK-47/AK-74 probably make up the majority of the world's military small arms only because the respective governments for their places of origin are also the world's largest arms dealers. The former Soviet Union spread AK's to every country and corner of the world that would embrace communism and the US has spread M16's to every country that embraces democracy. FMS and FMA are alive and well for the US, as are Russia, China and other country's arms selling/trading/lending/granting programs. It's really that simple...

With that said, I'll present the following food for thought:

Stoner's patent # US2,951,424 was issued on September 6, 1960. At the time, US patent law gave a 17 year patent validity period before it would enter the public domain, provided of course that all patent maintenance fees were timely paid, etc. (Today, a patent is valid for 20 years from the filing date) That means that Colt's rights to the direct-gas impingement system expired sometime in 1977, which by my calculation was almost 38 years ago. Considering that after expiration of Stoner's patent in 1977, ANYBODY could legally design a firearm with the DI system but nobody has other than US companies producing some variation (SR-25, AR-10, MRP, etc.) of the Black Rifle. With the sole exception of the Daewoo K1, I cannot think of a single example...and the follow-on Daewoo K2 got a long stroke piston. But I can think of plenty of small arms that have been designed since and that employ a gas piston in their design including the HK416, an arguable refinement of the M16 to make up for some of its shortcomings. But here are just a few examples that come to mind of other small arms that were designed with a piston:

AR18
Mini-14
Mini-30
Beretta AR70
FN-CAL
FN-FNC
SAR-80
L85
Holloway HAC-7
Leader Dynamics
HK G36
XM8
FN SCAR
SIG 540, 550, 556, etc.
SIG AMT
Steyr AUG
Chinese Type 87, 88, 95, 97, 03
Croatian APS-95, VHS,
CZ 556, 805
Madsen LAR
SAR21
TAVOR
Beretta ARX-160
Japanese Type 64, 89
Taiwanese T65, T68, T86
Poland MSBS
Magpul Masada/ACR
ARES Shrike/MCR
Ultimax 100
Robinson M96, XCR
Knight SCAR

I could continue, but I think you see where I'm going with this...

Both are a step in the right direction for a piston AR, but a fairly significant redesign of the upper is not the same as a piston retrofit kit, which was my original point.

As for the PWS, I don't see the small diameter thread-in pushrod as being very much support for the carrier, though it may simplify the design.

Yet the majority of those see little success.

Just because a gun uses a piston does not mean it's a successful design, and I mean XM8......really. You even listed the mini 14 whichhis laughable.

My reply was in regards to the most successful platforms using piston, well the two most successful platforms in the world are the AR-15 and the AK-47. Naming a dozen guns built using a piston does not make them successful, much less The most successful designs out there as was claimed.

All of my comments revolve around the fact that it was posted that the most successful individual rifles are piston.

Fair enough then, forget the short list that I offered of piston operated rifles. Also forget the reasons outlined in my first paragraph for why the AK and M16 are so ubiquitous. Forget that "successful" is quite subjective when comparing industry sales against government sales and free hardware; it's like saying that Bill Gates is broke when you compare his billions to the trillions of government taxpayer money.

So forget all of that for the purposes herein. How many small arms can you list outside of the various iterations of an M16 that are DI?

Only one that saw much service that I can think of offhand was the French MAS-49

I didn't bother listing the MAS-49 or the AG M/42 Ljungman because while they are direct gas operated, they're similar to the way that the Serbu BFG-50A operates in that they just dump their gases into a bored pocket that forces the carrier back with off-center thrust; not into a centerline thrust piston/cylinder arrangement like the respective AR15 bolt/carrier.

EDIT: I also didn't bother to list any of the normal sporting rifles manufactured throughout the world that are gas piston operated such as the Remington 742, 7400, 750, etc., Browning autoloaders, etc.
Any of these companies could have gone with a DI like the AR system after 1977 but none have, even though it's lighter, more economical to produce and certainly acceptable for the few shots fired in a hunting season compared to an infantry rifle. Why is that?

Well the M16/AR impingement system is pretty much one of a kind, so anything that uses that type of system is going to be a M16 variant

True, and I'm not here to bash on anyone or get into a flame war; I just think that it's a worthwhile topic to discuss instead of simply digesting that DI is the only way to go when there's plenty of global evidence to the contrary.

Great points by Ares, I think if not a higher grade materials and machining technologies used in present AR's production , a DI system wouldn't survive.
Always fun to see how GP haters bashing into a " AR piston systems " threads just to testify there is nothing to "fix" or improve over a DI AR

I still admire the CETME / G3 design with a non-rotating bolt and delayed blow back action. Simplicity and fewer moving / rotating parts.
The Johnson rifle being recoil operated was novel / innovative , way back in 1941.  

I like my rifles like my vehicles , with pistons.

Half of my ARs are piston , the other half gas.

I only shoot NATO ammo.

It makes no difference to me...UNTIL...cleaning time.

From another engineer:

Actually, the very first "assault rifle", the MP44 had a bolt carrier/spring/piston arrangement very similar to a piston AR.

If you look at an MP44 the large diameter spring is in the stock and in-line with the barrel axis and dictated a round profile receiver and bolt carrier.  The bolt carrier itself is a complicated shape, but at the very back, there is a semi-cylindrical surface that rides on the round receiver walls.  And the piston thrust line is well above the bore, higher than that of a piston AR.

But these were made out of steel.  Yeah, crappy low quality steel that Germany could get in 1943 and later.  The hard anodized 7075 AR upper is a better wear surface.

And the MP44 is not the only automatic designed from the outset with off-axis piston thrust.  The M1898 Colt machine gun, the Marlin Machine gun, just about every single barrel gas operated cannon 20mm and larger.  The M1917/1919 and M2 HB also have off axis spring positioning, relative to the barrel recoil thrust line.  The AAT-52 also has an off-axis spring relative to the thrust line if the bore.


[Original image http://www.gunpics.net]

The gas piston/DI debate kind of reminds me of "which motor oil" threads on many of the automotive and motorcycle forums.

Also, all bolt carriers tilt to some degree, even the regular AR.

Here is a diagram of a generalized bolt carrier and the forces on it:



Fp is the force from the piston
Fs is the spring
Fd is the drag force from the unlocking mechanism
Fr are the reaction forces resisting the tilting moment

Fp is in the 1000 to 1500 pound range.
Fs is in the 5 to 10 pound range.
Fd is in the .25 pound range.
The sum of the two Fr’s times their respective distances to the CG must equal Fp times its distance to the CG.

You can see that compared to the piston force the spring and drag forces are negligible and can be ignored.

The tilting moment is the force times the distance to the center of gravity.  Even in the regular AR the CG of the bolt carrier is not perfectly in line with the center-line of the bolt/piston, it's not off by much, but it is still off and there is a tilting moment.

Whether tilt becomes a problems has to do with the “wheel base” between the two reaction forces.  In the original AR the wheel base is only the front larger diameter.  This is more than enough to handle the minuscule moment from the internal piston, but when you switch to the larger moment imparted by a piston, the tilt becomes a problem with this short wheel base.  In the newer purpose designed carriers for piston ARs, the rear reaction force is moved back about 3.5 inches.



This not only reduces the load on the carrier guide surfaces, it provides a slope to guide the rear of the carrier into the receiver extension.

With a purpose designed carrier, bolt tilt is a non-issue.

Hey lysander, I just inspected the bolt in my LWRC piston AR, and it has exactly those alterations.  I hadn't thought about looking for something like that until your pic pointed that out.  I knew that LWRC had constructed the bolt and piston rod/key interface into a one-piece unit on this model, and my lower has an anti-tilt buffer setup.  Sounds like they've tried to cover all the bases.  I have a Steyr AUG (gas piston) and a PLR16 (gas piston), but this is my first AR with a gas piston.  I didn't really buy the LWRC because it was a gas piston design, but I love the rifle.  But then I also love my DI AR10's too.  I don't know...a good quality rifle is GTG regardless of which system IMO.

Proper maintenance of a rifle is paramount regardless of design. The only downside to pistons is they tend to run heavier located in the front and are subject to carrier tilt depending on weight.

The fat back-end has become the industry standard fix for bolt tilt.  It is simple and effective.

BUT the heavy duty op rod and piston in the MP44 is a 3rd point of contact for the carrier increasing stability, it's not just a floating rod as found in most AR piston systems.  The only similarity it has with an AR over an AK is the location of the action spring.
As you said in your next post, carrier tilt has been somewhat negated by increasing the tail diameter of the carrier, but that creates less room for error in manufacturing.  It's not really an issue until you throw a piston conversion in a mutt rifle that might have some buffer tube to upper receiver misalignment.  I've seen this exact thing first hand on more than one occasion with friends and at the range.  One was so bad that we had to mortar the bolt FORWARD because it basically locked up on the first shot.

I've built some fairly unique ARs, here's one that's DI, with a forward charging handle and forward action spring, similar to the ZM system, albeit beefier, but it's still DI and is one of my softest shooting rifles.
The gas tube and gas key are engaged throughout the full cycle and are very rigid, so they function as a forward guide rod and a 3rd point of contact.

You can still see from the wear marks on the MP44, it rubs a lot of the curved bearing surfaces.

If you look at the length of the fat back of the piston carrier, you can see that the swell rides in the upper until about 3/8" of the swell is in the receiver extension.

The ID of the extension is 1.000", the diameter of the back of a standard carrier is .930"The swell is only an additional .010" on the bottom.  

Receiver extension to upper misalignment bad enough to jam up a piston carrier, would probably not work too well with a standard carrier and gas system.

I guess reading comprehension is a skill we assumed you have. He outlined the very obvious reasons for that and you seemed to ignore it. Not to mention Eugene Stoner and others designed the piston driven AR18 which was superior to the AR15. By the time he had designed it the US military had already ordered the AR-15 and the rest is history.

The AR18 was designed in response to the fact that all the patents, for the AR15, were sold to Colt. Stoner was told to make another rifle but he wasn't allowed to use any of the same patents he had before, due to Colt owning them. The AR18 has its arguable shortcomings as well, which is true of any firearm. To state it is "superior" to the AR15 is a bit controversial.

It was also not developed for a "first world" nation, at the time, as it utilized sheet metal and stampings, similar to the Kalashnikov series of weapons. The AR18 was intended for emerging markets, if you look at the build design/materials.

All that being said, I'd love to see a new AR18, one made of forgings or billet, that uses a STANAG lower and a more modern rail system/flat top.

Just one thing to point out:

The AR18 (not solely designed by Stoner by the way) and its principle operating layout, has been copied a lot more that the AR15's principle operating layout.  I am not talking about carbon copy clones, but independent designs.

Due in large part to simplicity and cost of manufacture.

And, that is a bad thing?....


(It works too.)

Not necessarily, but along the same lines, greaseguns were easy to manufacture.
Would you rather be issued a greasegun or a Thompson as your service weapon?

I agree with Lysander here. Simplicity is also an argument used to favor DI, as there are "Fewer moving parts and a simpler design" to it.

Compared to the AR180?
More moving parts maybe, but those moving parts are a rod and a cup.

My apologies, I didn't make myself clear in the statement. I was meaning that the fewer moving parts in favor of the AR15 DI design. The AR180 has more moving parts and a different level of complexity there.

ETA: The closest thing to an AR180 I've gotten to fiddle with is the SCAR series. Isn't the same, obviously but the design is intriguing. I sold off my SCAR 16 but I think I may own a 17 one day.

We're on the same page.  My point was that the AR180 was simpler to manufacture and cheaper to manufacture than an AR15.

Of course, that was the point of the design. Stoner, and his team, knew they wouldn't be making any headway into the developed market, with the commercial success of the AR15. They made a decision to target a different market entirely, one that would be capable of manufacturing things with stamped metal and not forged. Hence the birth of the AR18/180 line.