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Old 10-07-2013, 12:30 AM   #11
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That is one of the biggest problems I can see with a piston AR. I wouldn't be able to repair a DI or piston AR myself anyway though...
maybe sometime in the future, as more piston system derived AR's become available, there will be more unversal parts fitment. right now, DI AR's are much easier to fix just about anywhere, with very few tools. most of the AR makers have pretty good parts availabilty and are pretty much universal, as long as they are Mil-Spec.
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Old 10-07-2013, 12:36 AM   #12
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AK-47s are gas piston, and their reputation for failing hardly sees the light of day. Putting together your own gas piston AR I could see how that would create problems, but a gas piston AR that was build from the ground up to be a gas piston AR by a manufacturer like HK, that's another thing completely I would assume.

I know I was talking about building your own, but just wanted to bring up the point.
the latest round of army trials ordered by congress showed that the entrants showed not even marginal improvement over the m4a1 in terms of reliability... these included the hk416 and scar16 and a few other piston driven entries
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Old 10-07-2013, 12:44 AM   #13
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I have personally never had a piston AR related malfunction, but obviously there are those who have. There are those on this forum who speak good and bad of both piston and DI AR setups who don't have a clue about what they are talking about. I have put a couple of my builds through the water torture test like HK does their 416, and both passed. Depending on what brand you go with, the aftermarket piston kits can run between $250-$500. I add JP buffer springs to my builds because I don't like that "sproing" sound, and I use BCM BCG's to insure quality. To the OP, I don't suggest you make a piston AR unless you are starting your build from the stripped lower out. Use a stripped barrel, then it makes it easier to assemble the operating rod assembly when you install the gas block. Moe hand guards are piston friendly, but be prepared to take a pair of snips to the heat shield, depending on which setup you use. I use Magpul furniture (handguards, pistol grip, and buttstock) 1. because they are high quality, 2. because they are more comfortable than basic M4 handguards and 3. to match the color shade. If you are planning to add a slide fire stock to your AR, a piston becomes a wiser choice than the DI system, as the piston slows the cyclic rate, reducing the likelihood of jamming. In that case, though, your AR starts becoming a defacto SAW, which is more fun, but less practical for SHTF. I just thought I would throw that factor in.
Bottom line, do your research. Don't take anyone's word for what a piston system or DI is or isn't. Go through the stickies and related threads on this and other forums of people who have experience, both good and bad, with various piston systems, go to youtube and see the installation videos, and then form your own opinion based on all the collective material you have gathered. I have good experiences with both systems, but I know there is crap out there with both systems.

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Old 10-07-2013, 12:47 AM   #14
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part of the problem with using a gas piston driven system in an AR is that many times the piston parts are proprietary, so replacement parts have to come from that particular manufacterer. with the DI system as long as you are using Mil-Spec parts, you have a much broader range of brands available for use as replacement parts.
From the brands I have installed, just about every part can be fabricated in a machine shop by someone with significant machinists skills. May not look the same, but it should work.
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Old 10-07-2013, 02:21 AM   #15
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AK-47s are gas piston, and their reputation for failing hardly sees the light of day. Putting together your own gas piston AR I could see how that would create problems, but a gas piston AR that was build from the ground up to be a gas piston AR by a manufacturer like HK, that's another thing completely I would assume. I know I was talking about building your own, but just wanted to bring up the point.
AK is a different animal. My brother in law bought a Stag that came with a CMMG piston kit, it's already leaking gas.
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Old 10-07-2013, 02:22 AM   #16
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AK is a different animal. My brother in law bought a Stag that came with a CMMG piston kit, it's already leaking gas.
How is an AK gas piston system different from an AR?
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Old 10-07-2013, 02:53 AM   #17
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How is an AK gas piston system different from an AR?
An AK was designed from the outset to use a full length piston that actually is attached to the bolt carrier, making it a very solid design. That carrier is kept aligned through its travel by rails for the full length if its travel ensuring that it moved straight backward and forward. As a bullet travels down the bore of the barrel by expanding gasses it passes a gas port that directs gas against the piston and drives the bolt carrier to the rear. As the carrier travels rearward it causes the bolt to rotate and unlock, and then travel rearward with the rest if the bolt carrier.

An AR with direct gas impingement has a gas block and tube that takes the gas that is tapped out if the barrel and directs it all the way sack to the bolt carrier through a gas key on top if the carrier and against gas rings on the tail if the bolt. This gas system reduces the amount if reciprocating weight as the action cycles. This contributes to better controllability under rapid fire and reduced felt recoil, as well as less variation in exact location and path if the reciprocating mass, which helps with repeatable accuracy. So, there are trade offs when picking one system over the other.

Adapting an AR to use a piston usually involves adding a gas block with a small intermediate piston or a floating piston that strikes a block on the bolt carrier that replaces the gas key. There are now more locations for gas to leak,ore moving parts, more springs, guides, etc. With some early systems shooters would notice a problem called carrier dip, where the piston striking the block on the carrier would drive the tail end if the carrier downward, causing drag inside the receiver or on the receiver extension going into the buttstock.
Since pistons weren't part of Stoner's original design, the aftermarket has found several methods for converting to a piston system, and that means there is no accepted standard in parts. As long as the company you select stays in business, then you should be able to get support, and parts. If they fold, you are stuck.

The good news us that ARs are so modular and easy to work in by just changing out components, that you could convert back to a direct impingement system just about as easily as dropping a new upper half onto the gun.

Also, the AR with its direct gas impingement system is a whole lot more reliable than most folks on the Internet give it credit. AKs do fail when dirty and neglected. They are actually harder to work on for major component replacement due to the riveting and machine pressed in parts, an AR can pretty much be completely torn down with hand tools, and no hydraulic presses or riveting machines are needed.
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Old 10-07-2013, 04:04 AM   #18
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An AK was designed from the outset to use a full length piston that actually is attached to the bolt carrier, making it a very solid design. That carrier is kept aligned through its travel by rails for the full length if its travel ensuring that it moved straight backward and forward. As a bullet travels down the bore of the barrel by expanding gasses it passes a gas port that directs gas against the piston and drives the bolt carrier to the rear. As the carrier travels rearward it causes the bolt to rotate and unlock, and then travel rearward with the rest if the bolt carrier.

An AR with direct gas impingement has a gas block and tube that takes the gas that is tapped out if the barrel and directs it all the way sack to the bolt carrier through a gas key on top if the carrier and against gas rings on the tail if the bolt. This gas system reduces the amount if reciprocating weight as the action cycles. This contributes to better controllability under rapid fire and reduced felt recoil, as well as less variation in exact location and path if the reciprocating mass, which helps with repeatable accuracy. So, there are trade offs when picking one system over the other.

Adapting an AR to use a piston usually involves adding a gas block with a small intermediate piston or a floating piston that strikes a block on the bolt carrier that replaces the gas key. There are now more locations for gas to leak,ore moving parts, more springs, guides, etc. With some early systems shooters would notice a problem called carrier dip, where the piston striking the block on the carrier would drive the tail end if the carrier downward, causing drag inside the receiver or on the receiver extension going into the buttstock.
Since pistons weren't part of Stoner's original design, the aftermarket has found several methods for converting to a piston system, and that means there is no accepted standard in parts. As long as the company you select stays in business, then you should be able to get support, and parts. If they fold, you are stuck.

The good news us that ARs are so modular and easy to work in by just changing out components, that you could convert back to a direct impingement system just about as easily as dropping a new upper half onto the gun.

Also, the AR with its direct gas impingement system is a whole lot more reliable than most folks on the Internet give it credit. AKs do fail when dirty and neglected. They are actually harder to work on for major component replacement due to the riveting and machine pressed in parts, an AR can pretty much be completely torn down with hand tools, and no hydraulic presses or riveting machines are needed.
Well I was talking about an AR that was built from the ground up to be a piston AR
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Old 10-07-2013, 04:43 AM   #19
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How is an AK gas piston system different from an AR?
The complements are not like for like between the two platforms. I get yet are both pistons, but the design of they AR is different from the AK
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Old 10-07-2013, 04:59 AM   #20
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Well I was talking about an AR that was built from the ground up to be a piston AR
Even starting with a stripped upper and lower its not designed to be a piston driven system. I firmly believe piston ar are a solution looking for a problem that never existed.

While they can be made to run well they just offer no real discernable advantage over a di gun made with the same care. At least ive never seen any quantifiable proof its better.
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