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Gas Piston vs. Direct Impingment

Discussion in 'Hunting & Fishing' started by turbocruiser, Oct 4, 2008.

  1. turbocruiser

    turbocruiser SILVER Star

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    Fellas, I feel like I've gotten as deep (in both the positive and negative senses of the word) into the gas piston vs. direct impingement argument as I possibly can however I'm still not settled on which mechanism would be best all around. If I was willing to part with 7K on one rifle right now it would be the HK 416 which uses the gas piston mechanism. However thats about 5K more than I'm willing to part with at the moment. I have carefully considered the SIG 556 which also uses the gas piston design but the strange thing with the SIG 556 is that although it is a gas piston design it also has adjustable valves which allows the operator to open the gas ports more in the event that powder fouling "restricts operation." I have always thought that the true gas piston designs are immune to powder fouling because they basically eject the gases, particulates and powders away from the action and not towards the action as most direct impingement designs ultimately do. I guess if I had to have a summary statement it would be that the typical direct impingement design of most AR15's and AR10's works well when lubed up liberally, and the typical gas piston design of most AK 47's and AK 74's works well regardless of conditions. Other than that one generally accepted guideline I have heard completely convincing arguments both ways about accuracy, reliability, simplicity and weight. After all the independent reading I've done I'd like to learn the wisdom of mud on this topic. So, y'all have any new thoughts on this old debate? Thanks. :cheers:
     
  2. Brian in Oregon

    Brian in Oregon

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    It's not just the gas system of the AK family that makes it more reliable than the M16 family. It's the entire design. The AK is built to much looser tolerances, which allow it to ingest a lot of debris and still function, as well as function over a much wider range of temperature extremes. The M16 is a better made, better quality, and generally more accurate weapon, but it is not as reliable. The M16 is also more complex and has many more small parts that must function within more precise tolerances than the AK. In fact, I'll state that there is nothing wrong with the M16 gas system PROVIDED it is kept clean. The bolt needs to be taken apart, detail cleaned, and put back together. If it's neglected, it can and will cause the gun to become very unreliable.

    So, the real question is, will one be in a scenario where it is not practical to do the proper maintenance and cleaning of an M16/AR15, and will be shooting such a volume of ammunition that failure can occur? If the answer is yes, then it might behoove one to install an op rod conversion, or simply go to a different weapons platform. But this won't get around the issue of reliability where precise tolerances are concerned. The AK simply wins, hands down.

    And I'm not slamming the AR15. I prefer them over the AK. I got rid of most of my Aks. I'm not worried about the AR gas system because I don't let my guns get that dirty.

    Now, if you want a trick to help keep an AR running, a trick that's cheaper than an op rod conversion, get a second bolt carrier and bolt assembly, and use it as a backup. Put it in the gun while you're cleaning the primary bolt. It's a good idea to check headspacing and accuracy. I would not do this, however, with a top of the line match barrel with a mated bolt head. But then, match guns are usually kept clean by competitors.

    Oh, one last comment. Some shooters install 22LR conversion kits in their guns. I am definitely not a fan of this, because the 22LR in quantity can plug the gas port. Ever try to clean the carbon from a 22LR from a compensator or muzzle brake? It's a nasty pile of fused carbon that's harder than glass. Get a dedicated upper for 22LR.
     
  3. lunyou

    lunyou

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    Not to act like I know what I am talking about or that I have had any experience with the SIG you mentioned but I haven't read alot of good about them.

    lunyou
     
  4. Brian in Oregon

    Brian in Oregon

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  5. turbocruiser

    turbocruiser SILVER Star

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    I haven't either, lots and lots of "meh" out there on this platform. I still don't understand the hybridization of the gas piston design and the direct impingement design of using a piston with ports that are adjustable? Is that just an extra extra extra measure of reliable operation or was it a workaround to another problem during design or during manufacture? I suspect knowing SIG that they removed the "loose tolerances" advantages of AK's and revealed the limits of that old design?



    Excellent link, thanks for that. I think I'm thinking too much about all this. I keep going back to the Rock River Arms LAR - 8 (.308 AR 10) but then I think myself out of it based on no chrome barrel and direct impingement design and the difficulty w/ doing a barrel swap due to the machining that they use. Perhaps the Armalite AR 10 A2-C is the best thing all around for me. Anyways, thanks for the link and for all the advice. :cheers:
     
  6. Brian in Oregon

    Brian in Oregon

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    And here's a dissenting opinion from another website, pointing out a potential problem....

    "Most piston retro-fit kits will fail on the AR-15. Most kits that do not replace the carrier gas key/bolt carrier eventually have failures due to the forces placed on the gas key screws. the screws crack and shear off while the weapon is cycling. Guns like the AR-18, HK-416 and SIG-556 have bolt carrier groups designed for piston drive. That is why they work flawlessly."
     
  7. yoda-g3

    yoda-g3

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    I bought a complete gas piston upper Bushy AR15. I'm assuming that this shouldn't apply to me right?
     
  8. cruiser100

    cruiser100 Comfortably Numb SILVER Star

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    There are two gas valve positions on the 556 refered to in the owners manual as "Position 1" and "Position 2". Position 1 is the normal position and should be used as much as possible. The only stated reason in the owners manual to use position 2 is due to gas block fouling. No gas passes to the action an the 556. The manual states that if you have to use position 2, the rifle should be cleaned as soon as is practical.

    The only time I've heard of anyone using Position 2 is due to using large amounts (1000's of rounds) of "dirty" ammo (I think it was some really cheap Wolf steel case). Quality ammo should not cause you any problems with this weapon.