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Thread: Help with a Gas-Piston

  1. #1
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    Help with a Gas-Piston

    I have a 16" POF Upper on a Bushmaster Lower. It now fails to eject at least three-times per mag. It was pretty low maintenance for the first year or so. I loved the design except for how hard it is to remove the gas piston.

    I have been emailing POF about it and they blame my use of surplus ammo and asked about the extractor.

    Others have said that it might be due to using M4 hand-guards and not a more open rail system.

    It seems clear to me that it is not the extractor but the bolt failing to cycle fully. The empty casing is being extracted, but the bolt is only cycling far enough to get bend the firt round without ejecting the casing. Basically it is stove-piping the casing while trying to load the next round.

    If it's the hand-guards or the ammo, then this isn't the weapon for me.

    No Direct Impingement system I have owned or been issued has ever given me any reliability problems. Many of them have undergone much more abuse as well.

    Maybe I am cleaning or lubing it wrong? My practice has always been to keep the weapon as dry as possible (light coat: barely oily to the touch) and to avoid lube completely on gas pistons.

  2. #2
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    Regardless of who makes it all ARs need oil even piston designs. One of the few guns you can run dry is the AK and a piston AR isn't an AK.

    Does this ammo cause any problems in any other ARs that you may own?

    To test for enough power: Put one round in a mag, load the round from the mag and fire the round.

    Did it eject and lock the bolt back?
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

  3. #3
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    Quote Originally Posted by demigod View Post
    The AR piston systems out and about these days are much more problematic than a properly built DI.

    Sure. You hear a lot of issues with the DI. But there's so much bad aftermarket junk rifle components/builds and shitty Imported ammo out there right now, the notion that there's something lacking with DI is greatly exagerated.
    With a caveat: factory H&K 416's just run.

    Remember the utlity of an AR piston design:

    if you run a barrel shorter than 14.5"
    if you run suppressed
    if you run a wide variety of ammo
    if you run extended full auto

  4. #4
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    I have fired the 416 and was highly impressed. I watched several thousand rounds go through one in one day with nary a glitch. Having said that. I would not use one in the sandbox until I could run it through the paces in country where shit generally wants to break instead of the range.

    Quote Originally Posted by demigod View Post
    I'll take your word on that. I've never seen one.
    But many of the commonly available kits/completes still have "bugs" to work out. Amercian companies should do a better job of ripping of HK's design.

  5. #5
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    Just to confirm

    Quote Originally Posted by Thekatar View Post
    With a caveat: factory H&K 416's just run.

    Remember the utlity of an AR piston design:

    if you run a barrel shorter than 14.5"
    if you run suppressed
    if you run a wide variety of ammo
    if you run extended full auto
    Forgive me, but just to confirm....

    You're saying that an AR piston set up is good if.....(all of the above)

    Or

    You're saying that an AR piston set up is not good if...(all of the above)

    The reason I'm asking is because I've ordered a BM gas piston upper (complete upper). There's a 6 week backlog...and I'm wondering if I should tell them to forget it.

  6. #6
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    Quote Originally Posted by Veracity View Post
    Forgive me, but just to confirm....

    You're saying that an AR piston set up is good if.....(all of the above)

    Or

    You're saying that an AR piston set up is not good if...(all of the above)

    The reason I'm asking is because I've ordered a BM gas piston upper (complete upper). There's a 6 week backlog...and I'm wondering if I should tell them to forget it.
    Each one is an independent consideration or justifiable need for the piston. However the more of those requirements you check off, the more viable the piston design.

  7. #7
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    Quote Originally Posted by thetallengineer View Post
    Each one is an independent consideration or justifiable need for the piston. However the more of those requirements you check off, the more viable the piston design.
    What he said.

  8. #8
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    Quote Originally Posted by gotm4 View Post
    Regardless of who makes it all ARs need oil even piston designs. One of the few guns you can run dry is the AK and a piston AR isn't an AK.

    Does this ammo cause any problems in any other ARs that you may own?

    To test for enough power: Put one round in a mag, load the round from the mag and fire the round.

    Did it eject and lock the bolt back?
    The ammo is reliable in other ARs.

    The bolt locks back fully almost half the time. Now I know that the bolt and bolt carrier need a light coat on metal to metal areas. But the piston? Maybe I am just too used to old machine guns, and AKs, where the piston needs to be dry...

    For all it's advantages, even when it's working properly, I see it as no real improvement to a DI gun.

  9. #9
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    Quote Originally Posted by Hluill View Post
    The ammo is reliable in other ARs.

    The bolt locks back fully almost half the time. Now I know that the bolt and bolt carrier need a light coat on metal to metal areas. But the piston? Maybe I am just too used to old machine guns, and AKs, where the piston needs to be dry...

    For all it's advantages, even when it's working properly, I see it as no real improvement to a DI gun.
    The piston should be run dry but the bolt carrier and cam pin should be wet with lube.

    What brand of ammunition are you using?
    What magazines are you using?
    Do you have the older kind of carrier where the carrier key is screwed onto the carrier?
    What's the length of your buffer spring?
    What buffer are you using (CAR/H/H2/H3 etc.) ?
    Is is possible that carrier tilt is tearing up your receiver extension (buffer tube) ? Which might be slowing the carrier ?

    If you have another AR or a spare known good bolt I would recommend trying that along with a known good buffer spring and CAR or H buffer.
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

  10. #10
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    Have you cleaned the ejector? Removed it to see if there's any crud in the tunnel? Put a couple drops of CLP in there and work the plunger back and forth?

    Sounds like extraction is working fine, you're just not getting the cases ejected. Either the case is trapped in a "too tight" extractor hook or something is impeding the ejector working. Just a thought.

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