DI vs piston for AR

KDX

KDX

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I know it's probably a dumb question to be asking but I know next to nothing about the AR platform. What are the advantages/disadvantages of the DI and the piston systems? Thanks in advance.
 
Piston systems:
- chamber stays cleaner
- heavier
- some say more reliable
- much of the spent gas ends up outside the receiver
- more expensive
- no standardized piston system so all brands have different parts

DI Systems:
- chamber gets dirtier
- lighter
- much of the spent gas ends up inside the receiver
- cheaper
 
Some less important diffs that make little to no difference in Canada

- If you plan on underwater activities there is less issues with a piston as there is no gas tube to fill with water and rupture.
- If you get to fire sustained full auto there is no risk in a piston of the gas tube heating and rupturing or fouling.
- If you use NV there is less issues with blooming on a DI as the heated gas is vented into the reciever and not by the piston behind the front gas block which is generally ahead of the NV receptors.
- Due to less heat in the reciever with a piston system the reciever is more reliable under sustained fire and less prone to failures which increases the longevity of the bolt and assemblies.

None of this is an issue for 5 rnd paper punching.
 
Piston A.R.

The dirt still exists - but at the front where the excess gas is vented,
Also - the piston block and handguard front gets very hot.

Some systems have carrier tilt problems causing buffer tube wear.
swingerlh.gif
 
DI has a slightly longer clean-time, and is supposedly more prone to the "difficult" carbon-caking....;)....that said, I have a Swede AG-42B reachambered with .308 M-14 "guts", and it's DI as well.....no problems thus far?.........:wave:
 
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Which ever gun has the best barrel (as well as other components) will be the most accurate, does not have much to do with the extra weight of the piston system.
For a 5 round semi auto a DI gun is fine. Some people just want different more interesting guns, that have some advantages, even though they may never take advantage of them.

Rich
 
DI is way more practical for the average shooter... people who are worried about carbon in their guns shouldnt be too worried... the average AR will run through a few thousand rounds before you should have any serious problems.
 
We have some DI SR-16E3's that have gone over 35,000 rds without being cleaned, on the same bolt and barrel ;)

Pistons are fine in weapons designed from the ground up for a piston; Sig 55x series, Hk G36 (albiet need a better barrel trunion mount) FNC etc.

Pistons in AR's are a FAIL.
 
KevinB said:
We have some DI SR-16E3's that have gone over 35,000 rds without being cleaned, on the same bolt and barrel ;)

Pistons are fine in weapons designed from the ground up for a piston; Sig 55x series, Hk G36 (albiet need a better barrel trunion mount) FNC etc.

Pistons in AR's are a FAIL.
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More details, please?.....:)

My sole experience with DI before the AR-180 was with a 7.62 DI....:yingyang:
 
KevinB said:
We have some DI SR-16E3's that have gone over 35,000 rds without being cleaned, on the same bolt and barrel ;)

Pistons are fine in weapons designed from the ground up for a piston; Sig 55x series, Hk G36 (albiet need a better barrel trunion mount) FNC etc.

Pistons in AR's are a FAIL.
Click to expand...

:agree: End post ;)
 
Comparing the AG42B, Hakim, MAS 49 with the AR is misleading.
The first three are DI.
The AR is not. Its operating system is different.
It uses a ducted gas operating system; gas is ducted back into the bolt carrier, where there is an expansion chamber. Gas expanding in the chamber forces the bolt carrier and bolt apart. This gives rearward motion to the carrier and rotates the bolt to unlock. This is why there are piston rings on the bolt, and gas escape ports in the carrier. The AR system can contribute to fouling inside the carrier, not in the chamber.
In the first three, the gas tube forms a bit of a nozzle which engages the bolt carrier. The bolt carrier is blown back off the gas tube extension.
If the passageway inside the AR bolt carrier key were blocked, so that gas could not enter the expansion chamber inside the carrier, the system would be like that of the AG, Hakim and MAS. But would it even work?
A major advantage of the AR ducted gas system over the AG and MAS is that the operating system is able to compensate somewhat for ammunition variation. The Hakim has a valve, the AG and MAS don't. Lack of adjustement or compensation makes a design rather ammunition sensitive.
 
Dsiwy said:
:agree: End post ;)
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The same type of people who wouldn't accept M16 over the M14s initially as they were toy models and said no polymer frame pistol would ever replace the steel frame.

While currently DIs have a certain advantage due to the standardization of parts it's telling that there are no new rifle platforms being designed with direct impingement technology. It will be around for quite some time for sure but the process for eclipsing it began a long time ago.

Respectfully, those that hold out that the direct impingement system is the past, present, and forever of small arms aren't considering history. It's an evolutionary process, and advances in technology are both inevitable and welcome.

The piston gun cleans up in far less than half the time of a DI gun when more than twice as dirty with ZERO carbon scraping of any surface whatsoever. To me, that is a vast improvement and makes tremendous sense.

Having owned both I haven't found anything that my DI guns can do better than my piston ones but the same cannot be said the other way around.

And athough not an AR in the strictest sense it's as close as poop is to swearing; isn't the new KAC PDW a piston based carbine? HK 416 which was specifically designed to be an improvement for the AR's failings?
 
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incorrigible said:
The same type of people who woundn't accept M16 over the M14s initially as they were toy models and said no polymer frame pistol would ever replace the steel frame.

While currently DIs have a certain advantage due to the standardization of parts it's telling that there are no new rifle platforms being designed with direct impingement technology. It will be around for quite some time for sure but the process for eclipsing it began a long time ago.

Respectfully, those that hold out that the direct impingement system is the past, present, and forever of small arms aren't considering history. It's an evolutionary process, and advances in technology are both inevitable and welcome.

The piston gun cleans up in far less than half the time of a DI gun when more than twice as dirty with ZERO carbon scraping of any surface whatsoever. To me, that is a vast improvement and makes tremendous sense.

Having owned both I haven't found anything that my DI guns can do better than my piston ones but the same cannot be said the other way around.

And athough not an AR in the strictest sense it's as close as poop is to swearing; isn't the new KAC PDW a piston based carbine? HK 416 which was specifically designed to be an improvement for the AR's failings?
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This is not about DI vs Piston, but rather companys trying to make a AR platform into a very pricey piston POS. This is lost on civi shooters since they do not use the weapons as much or in adverse conditions. Sofar all Piston ARs have problems even the ultra awesome HK :p
 
incorrigible said:
The same type of people who woundn't accept M16 over the M14s initially as they were toy models and said no polymer frame pistol would ever replace the steel frame.

While currently DIs have a certain advantage due to the standardization of parts it's telling that there are no new rifle platforms being designed with direct impingement technology. It will be around for quite some time for sure but the process for eclipsing it began a long time ago.

Respectfully, those that hold out that the direct impingement system is the past, present, and forever of small arms aren't considering history. It's an evolutionary process, and advances in technology are both inevitable and welcome.

The piston gun cleans up in far less than half the time of a DI gun when more than twice as dirty with ZERO carbon scraping of any surface whatsoever. To me, that is a vast improvement and makes tremendous sense.

Having owned both I haven't found anything that my DI guns can do better than my piston ones but the same cannot be said the other way around.

And athough not an AR in the strictest sense it's as close as poop is to swearing; isn't the new KAC PDW a piston based carbine? HK 416 which was specifically designed to be an improvement for the AR's failings?
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Problem is, piston isn't THAT much better then a DI and the DI has it's own benefits. And piston isn't a new idea; Eugene Stoner himself designed AR-18 as a lower costing alternative to the AR-15. The long stroke piston was found on the M1 Garand.

So there's nothing evolutionary or revolutionary about turning an AR15 into a piston design. You're just swapping one established system for another, taking one set of compromises and trading it for another. You just have to decide which compromises are acceptable to you.
 
As a beginner AR shooter I thought long and hard about what my first rifle was to be and DI or Piston was a big part of it. After countless forum reads I finally settled on a piston system. It turned out that the company I wanted to buy from (LMT through Queststar) had a shipment of DI's coming in much sooner than I could get an LMT Piston system so I bought it. I shoot the rifle quite a bit, after reading about all the cleaning that needs to be done, gas inside, and carbon buildup, I thought that maintenance would be much more difficult than it is. It's not hard to keep it clean and I believe if you buy a quality piece it will eat up anything you want to run down the barrel. That being said I'm not running 1000's of rounds a week through it but just having fun at the range and some 3 gun matches.

Go quality and either system will be ok, don't be afraid of DI if you get a deal, they have been around a long time and will continue to be because they get the job done.

Hope that helps,
 
KevinB said:
We have some DI SR-16E3's that have gone over 35,000 rds without being cleaned, on the same bolt and barrel ;)

Pistons are fine in weapons designed from the ground up for a piston; Sig 55x series, Hk G36 (albiet need a better barrel trunion mount) FNC etc.

Pistons in AR's are a FAIL.
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Please explain.
 
Antoine22 said:
Please explain.
Click to expand...

http://xcrforum.com/index.php/topic,3956.0.html


The biggest overall problem with Piston AR's is Carrier tilt.

Why is there tilt? There is tilt because Gas Piston AR's (GP-AR's) do not have a carrier key that is a gas tube like on DI-AR's (regular AR, Direct Impingement AR's). The carrier key of a GP-AR is a solid so the piston has something to strike to move the BCG (Bolt Carrier Group). Since the piston is striking the BCG from the top and off axis (off-center), it causes the BCG to enter the buffer tube at a downward angle. DI-AR's does not have carrier tilt because as the gas enters the bolt carrier key, it is bled off and the BCG enter's the buffer tube straight in. GP-AR's piston action strikes the carrier like a hammer, therefore causing tilt.

Picture of LWRC M6A2 BCG showing the filled in Carrier Key



Why is it bad for the BCG to enter the buffer tube at a downward angle? The pic below shows why it is bad. This is a pic of a LWRC GP-AR that shows major buffer tube wear from Carrier Tilt. The BCG took off a lot of metal from the buffer tube on this gun. This is not a pic of my gun, all I know is it is from a LWRC rifle that I found on the LWRC forum. Most likely it is from a M6A1 or older since my M6A2 does not seem to have carrier tilt at all. Amazingly though, carrier tilt does not seem to affect the operation of the gun one bit as stated from the person who took this pic.



Here is a pic of the rear of my LWRC M6A2 bolt. As you can see it is different than a normal DI-AR BCG, in that the LWRC M6A2 BCG is channeled and ramped to help aid in entering the buffer tube smoothly. The ramps seem to help a lot as I have not notice any shaved metal on my Buffer Tube like in the picture above. I am not sure why there are channels, my guess it takes away more contact points from the the BCG, to prevent it from contacting the sides and top of the buffer tube and shaving more metal at those places. Also notice how the the buffer tube is staked. Staking the buffer tube is not that important on a DI-AR, but is very important on GP-AR's because carrier tilt causes the buffer tube to work harder. No staking on the buffer tube means it is very likely to come loose.



Another problem with GP-AR's is they cause the gas key screws (screws that hold the bolt carrier key) to also work harder. Keys have been known to come loose and even break on LWRC rifles. LWRC did not stake keys on older rifles but the M6A2 now has staked gas keys. However, the stake keys did not seem to stop the keys from breaking as guys are still reporting broken keys on LWRC M6A2 rifles on the various forums. LWRC has moved to the one-peice carrier for the M6A3, much like what you see on Rugers and Adam Arms GP-AR BCG's (see picture below). As of date though, the new LWRC one-peice BCG is not available to the general public as a replacement piece, only available on new rifles.

Picture of LWRC M6A2 2-piece BCG with cross-staked key


Picture of Adam Arms one-piece BCG



*Comment on Cross staking: I am not a big fan of cross staking, but I have a buddy who is a machinist and he told me cross-staking is a legitimate way to stake screws to keep them from rotating. He said if you look closely, you can see the metal from the screws actually flare out against the surrounding metal to help keep the screws from rotating.


As you can see the firing pin is fully shrouded (covered) on a LWRC M6A2 BCG. This is important because if carrier tilt is excessive enough, the trigger hammer might rub up against the BCG, and if firing pin is not shrouded, then the hammer would wear against the firing pin. These days almost all AR's both GP and DI, seem to be fully shrouded.



My LWRC M6A2 carrier above has only seen about 400 rounds and shows no sign hammer wear on the BCG. Not only that but it shows no metal shavings on the buffer tube either, as I already mentioned 2 times. But I will mention it again just in case you guys did not pick that up Wink.

My rifle does not seem to have carrier tilt, but one bad thing I did notice on my LWRC is the BCG seems to be striking the buffer tube abruptly like the way a hammer strikes a nail. The reason I say this is because my buffer has beat up marks and dents as shown in the picture below. My DI-AR's (Bushmaster, Noveske, and AR-10's) DO NOT have this problem.



Conclusion:
So what's the final verdict on GP AR's? They do run cooler and cleaner, but the action on them seems to be very rough as evident by all the dents and shaved metal everywhere. LWRC has worked out most of the bugs, and I am sure they will work out all of them to make a better rifle. However, that does not take away from the fact that the makers of GP-AR's took a simple working DI-AR and made it more complicated. Stoner is no dummy, if he felt the AR needed a GP he would have put one in. If you really wanted a cleaner and cooler weapon I would just buy one that was designed from the ground up to run a piston, such as an XCR or SCAR, or even older designs such as an AK or FAL.
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This conversation is very cute.

I'd like more info on the Marines IAR testing.
They sure don't think that an AR Piston = Fail.
And I'm sure they shot the Shat out of their test guns.

They are going forward with the HK 416 with a heavy barrel.

Rich

PS: A generation ago, the masses said that the M16 DI was Shat and the
M14 was "all that" and would live forever.
 
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