Why Gas Piston over Direct Impingement?
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Old 10-15-2010, 11:56 PM   #1
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Default Why Gas Piston over Direct Impingement?

I'm very very green when it comes to ARs, M16s, AKs, ACRs, etc. So bear with me. I want to build an AR15 sometime in the beginning of next year (when finances allow), but it's lead to a very interesting debate I didn't know existed, why would you choose gas piston over a direct impingement system?

I was reading about the Bushmaster ACR (and watching the future weapons episode) and noticed they went with a piston system, and then boasted that their rifle was half a pound lighter than it's M16 counterpart. If weight was such an issue wouldn't you go with DI instead?

What advantage does a piston system have over DI? many of the people I know have said it's largely a solution to a problem that doesn't exist. Both systems require cleaning and regular maintenance, it's not like the piston system never gets fouled up. If you took care of your rifle like you're supposed to, is there ANY advantage? For people like me who will likely never see combat, nor spend weeks at a time firing off shots without cleaning my rifle, is there any good reason to go with a piston system?

I'm just trying to wrap my head around why magpul would design the assault rifle of the future and then slap a piston on it. What am I not understanding?

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Old 10-16-2010, 12:07 AM   #2
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Because gas piton doesn't jam up form dirt and muck like gas impengimet does when it can really count. Yeah, you potentially sacrifice some accuracy but you get reliability in return.

Just my 2 cents worth.

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Old 10-16-2010, 12:59 AM   #3
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I'm just riffing here, but hear me out. Given the direction of gas flow, the only way for muck to get into your gas return system is to have it chambered in front of your round and fired through the gas tube, right? Well if there's so much dirt, sand, or mud on your bolt/in your mag/in your receiver that it clogs your gas tube, your rifle is probably going to fail as a result of your follower or bolt getting stuck anyway, regardless of which system funnels gas back to the debris-clogged receiver....

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Old 10-16-2010, 02:45 AM   #4
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This argument can go 'round and 'round for days, so I will try to take some of the steam out of it with this explanation, not saying I will be successful... LOL

The Direct Impingement system is the way the platform was designed. It harnesses gas from the round and directly cycles the bolt/action.

When the M-16 went to Vietnam, there were complaints that it would not work well if dirty/muddy.

Changes were made, education was initiated and the weapon system moved forward.

At the same time Good Ol Mikhail over in Mother Russia had developed the AK platform, which was a knock off/copy/ hommage to a German design.

Ths system is a piston, or op rod, type platform. The gas is harnessed near the bore and it drives a piston to cycle the action. As there is less overall travel of gas, the "piston" or "op rod" covers the distance with solid metal and does not allow the same kind of dirt/mud/grime.

Wars come and go, AK's come to the states, people start getting interested and then we have the AK vs. AR battles/tests/comparisons.

Someone got the idea of why not combining what is great about the AK, the fact that it will run no matter where you are deployed, with the more familiar AR platform.

There was money to be made - need I say more?

From a very novice gunsmith wannabe standpoint, you get this:

The AK is not as accurate as the AR - regardless of who made each model. If you compare skill level of maker to skill level of maker, the AR is more accurate. The piston system of the AK causes flex in the barrel with each follow up shot, so accuracy is compromised past shot one.

Adding a "piston" to an AR does the same thing. It is "more reliable" but you are losing accuracy because of the way the cycling of the action must work, you have harmonics along the barrel.

At street to street, house to house type of fights will this affect the "average" shooter?

NO! Absolutely not. Out to 50 yards, Minute of Bad Guy is going to be Minute of Bad Guy unless you are trying for a head shot.

At 200 or 300 yards?

Yes! A hit with a DI AR might not be a hit with a piston AR. Not that you can't get man sized hits, you can, but the DI is going to be more accurate.

So, you want to build one. The Piston versions are more expensive currently so if cost is a factor, and I guage that it is by your post, it is going to be cheaper to build a DI edition.

Personally??

I live in the Pacific Northwest. We get rain, wind and usually blowing pine needles and "junk" about 8 months out of the year. Now, I have never gone on a three day creep with my AR, or put a lanyard on it and pulled it through a swamp, followed by a sandbox, followed by a wet concrete pour, but I have never had weather conditions cause my weapon to stop working.

Could it happen? Yes. If you do not take care of your equipment, any piece of equipment can fail, for the most part.

For most folks, the benefit of the AK has always been it will run dirty, cold, wet anywhere on the planet and keep heads down with that distinctive chatter.

In my mind the benefit of the AK has always been the heavier round. Why take the negative, the piston/op rod, and keep the smaller, less powerful AR cartridge?

I feel the Piston AR's are a solution where the problem was created by people Rube Goldberging something to death.

Good luck and feel free to PM if you have further questions on a build.

JD

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Old 10-16-2010, 03:41 AM   #5
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As somebody who has one of each, I'm less dazzled by the piston setup now than I was before I had one. There's more felt recoil with a piston as well as whatever accuracy issues there may be. I was planning on my next build being another piston, but I'm slowly coming back to a DI setup instead.

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Old 10-16-2010, 03:14 PM   #6
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Quote:
Originally Posted by Dillinger View Post
There was money to be made - need I say more?
JD
That says it all right there.

In it's infancy, the M16 got it's (deservedly) bad reputation because of two reasons. The original ammunition was loaded with a particular ball type powder that left a lot of nasty gunk in the gas system and receiver that caused stoppages. The other problem was that troops were not even issued cleaning kits for these rifles in the beginning stages of Vietnam.

After changing to a stick type powder which burned much more cleanly and issuing cleaning kits for the rifles, those issues went away for the most part. But the bad rep has lived on.....

I've got a couple or three AR's and have shot the snot out of them. Have never had a stoppage or any problem with a crud buildup in any of them using the standard gas system. Granted, I don't drag them through mud and sand. If you plan on abusing a rifle, I'd go with a real AK.
JMHO.
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Old 10-16-2010, 03:33 PM   #7
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I usually don't post much in the AR section, but having worked extensively with both types of gas systems in different platforms, here is the short of it.
DI System in the AR imparts heat to the bolt carrier and bolt each time it is fires and under sustained fire, can get quite hot. It also vents the gasses into the reciever which causes undue fouling. If not properly maintained and lubed (you all know what proper lubing of an AR is, right?), "it will cause stoppages just when you need it the most".

The Gas Piston system vents it's gasses outside of the reciever and imparts no heat to the bolt group. Other than the barrel getting hot under sustained fire, the reciever and bolt group stays cool to the touch and is not fouled by the powder gasses. Therefore the bolt and carrier requires less frequent lubrication and cleaning and the rifle will be more reliable.

I have seen no real differences in accuracy in virtually identical rifles, using both systems.

The inherent problems with the DI system will usually not affect the average shooter. Stoppages will, however, show-up in competitions with sustained fire and in extreme field conditions, or in rifles not maintained properly.

Without a more detailed and lengthy write-up using many test results, photos, etc., that is the jist of it.

Either system will serve you well.
Hope this helps and heads off a long debate on the issue. I tried to make the compairison as simple as I could without being to lenghly.



Jim.........................

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Old 10-16-2010, 04:34 PM   #8
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Can't add to much to this. At the end of the day bubba its all about your personal preference and financial status. For all intentive purposes, "they all kill the same."

Why pay extra if you can get a bang stick to do the same job for less?

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Old 10-19-2010, 01:07 AM   #9
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Thanks for the help gentlemen. So it seems like a piston system is more appropriate to close combat where th accuracy issues are less relevant, when long periods between cleanin are more common, and drity environments and ammunition are present. But for civilian purposes there's no distinct advantage?

I was thinking more about why the acr was made with a piston system and the guy on future weapons made it seem like its great advantage over the m16 was how easily it could convert to a non nato round for covert ops. If that's true, isn't it possible then that you're using ammunition made with the dirtier powder? If that's the case and you're working largely with battlefield pickups, then might a piston system make more sense?

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Old 10-19-2010, 01:20 AM   #10
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Quote:
Originally Posted by urban View Post
its great advantage over the m16 was how easily it could convert to a non nato round for covert ops. If that's true, isn't it possible then that you're using ammunition made with the dirtier powder? If that's the case and you're working largely with battlefield pickups, then might a piston system make more sense?
Huh?? You lost me there?

If by "non-Nato round", you mean civilian ammo here in the states, I don't think it's an issue.

How many rounds are you talking about putting down the barrel, honestly, without taking some time to clean the weapon?

The reason I ask, and I am serious, is that we see guys come into the shop from Pierce County SWAT who train A LOT and they put TONS of rounds through their weapons on both full auto and semi auto fire. While they do take care of their weapons, frequently their weapons would not qualify as being of the "best" in care and maintanence.

We see a weapon go 8,000-10,000 rounds and need a new gas tube and probably some rings. Perhaps a new recoil buffer spring here or there, but generally if a weapon comes in for a failure to cycle, there is a CLEAR reason when you take it apart and start looking into it.

These are weapons that are shot frequently and with sustained fire.

I just find it hard to believe that in a urban battlefield scenario a person is going to be shooting THAT MUCH without a time to let the weapon cool and to be able to clean it.

You would probably end up dead from exhaustion and/or dehydration first.

JD
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