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Thread: My 14.5 Mid-length doesn't like 55gr.

  1. #21
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    Keep what I'm about to say on the level of second-hand information, but it might spark an idea among the experienced armorer's here: If my memory serves, the 14.5 mid-length configuration, having perhaps less barrel length to the muzzle after the gas port than is ideal, is more finicky with ammo, particularly underpowered, lighter bullets. FWIW.

    John
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  2. #22
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    Quote Originally Posted by Iraqgunz View Post
    Knowing these facts I am thinking that the gas port is wrong, the gas tube is burned out or excess leakage at the FSB. Nothing else makes sense and if the bolt and carrier assy. has worked in another rifle w/o problems and the mags have been checked then that's all it can really be.
    I agree. But I would like to know which gas block he has or if it's a FSB (A frame).
    Testing with known good pressure ammo will make sure it's just not some weakass rounds. I have some PMC and Radway Green that won't even run in a 16" CAR length Colt nor a 20" rifle unless used with a supressor.

    He'll likely have to open up the gas port about .005" if even with know good ammo it still doesn't work. I don't like to open a port unless it's absolutely necessary.
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

  3. #23
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    M4,

    Not sure if you knew this but the U.S Miltary issued a NAR (Notice of Ammo Reclassification) back in 2005 which specifically told units not to use the Radway Green in M4 carbines and went so far as to restrict it to training use only. I will gladly send a copy of that to you. Though it is NATO spec ammo, it was designed to be used only in the SA80 rifles and not in the M16 FOW.

    Yes, ammo could be the culprit though I thought that was ruled out earlier? We had a gun here recently that was having problems as well. It had an unidentified 16" barrel and flat top upper. The person in question had a regular carbine buffer spring and an H2 buffer. I suspected it was not running due to the buffer so I replaced it. Still malfunctioning. Because this guy was not on the project and had limited support I did an overhaul and replaced his rings and extractor as well. Still would not run. So I slapped a gas tube in real quick and now it runs like a champ.

    Quote Originally Posted by gotm4 View Post
    I agree. But I would like to know which gas block he has or if it's a FSB (A frame).
    Testing with known good pressure ammo will make sure it's just not some weakass rounds. I have some PMC and Radway Green that won't even run in a 16" CAR length Colt nor a 20" rifle unless used with a supressor.

    He'll likely have to open up the gas port about .005" if even with know good ammo it still doesn't work. I don't like to open a port unless it's absolutely necessary.

  4. #24
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    Quote Originally Posted by Iraqgunz View Post
    M4,

    Not sure if you knew this but the U.S Miltary issued a NAR (Notice of Ammo Reclassification) back in 2005 which specifically told units not to use the Radway Green in M4 carbines and went so far as to restrict it to training use only. I will gladly send a copy of that to you. Though it is NATO spec ammo, it was designed to be used only in the SA80 rifles and not in the M16 FOW.

    Yes, ammo could be the culprit though I thought that was ruled out earlier? We had a gun here recently that was having problems as well. It had an unidentified 16" barrel and flat top upper. The person in question had a regular carbine buffer spring and an H2 buffer. I suspected it was not running due to the buffer so I replaced it. Still malfunctioning. Because this guy was not on the project and had limited support I did an overhaul and replaced his rings and extractor as well. Still would not run. So I slapped a gas tube in real quick and now it runs like a champ.
    Yeah I do have a copy of that as well.
    I didn't see where he mentioned what 55gr besides Q3131 and PMC that he tried (I could have missed that) those two are known to be weak.

    If he had said it still short stroked on XM193, LC or WCC M855 or Win Q3131A then I would say it's surely a gas leakage problem or too small of a gas port.

    Grendelizer,
    Dwell time is sufficient but the gas port size is likely too small. Noveske makes 14.5" midlengths and they work very well. My wife has one that was cut to 13.6" or 13.7" (which was a 14.5" Afghan a midlength) with a AAC SOCOM flash hider M42000 mount perm. attached for an overall length of 16" and it works great with a suppressor and without. Randall of www.ar15barrels.com shortened it and opened up the gas port .

    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

  5. #25
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    It has a fixed front sight base.

    I'm going to have the gunsmith look at it. I've come to the conclusion now that it's definitely the gas port, or something to do with the gas system on it.

  6. #26
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    A word of caution. Verify that your local "gunsmith" has a good working knowledge of the AR system. I would buy a small quantity of known quality ammo and see what happens. If it still fails replace the gas tube. This is fairly easy and it costs about 10.00 dollars. If it fails again, then I would take it in. This is probably the simplest and least expensive route.

    Quote Originally Posted by fireftrjef View Post
    It has a fixed front sight base.

    I'm going to have the gunsmith look at it. I've come to the conclusion now that it's definitely the gas port, or something to do with the gas system on it.

  7. #27
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    Ok, I was just looking it over since it has LaRue FF rails I can easily look over the gas tube, and noticed residue on the outside of the gas tube where it enters the FSB.

    It easily came off by rubbing it with a dry Q-tip. Probably 1/4" back the gas tube is clean.

    Does that indicate a leak?

  8. #28
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    Quote Originally Posted by fireftrjef View Post
    Ok, I was just looking it over since it has LaRue FF rails I can easily look over the gas tube, and noticed residue on the outside of the gas tube where it enters the FSB.

    It easily came off by rubbing it with a dry Q-tip. Probably 1/4" back the gas tube is clean.

    Does that indicate a leak?
    Some leakage there is normal.

    Since you said it's a factory Sabre Defence upper and now you said it has a LaRue.....who installed it?
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

  9. #29
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    The gunsmith installed it. But I'm just going to take it back to him and have him to get it right.

  10. #30
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    My only concern is that Mr. Local Gunsmith jacks it up more or snows you over as recently happened to someone here when he went to have his lower engraved. I would take notes from what has been posted here and bring them with you when you speak to him.

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