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Thread: Opened up Gas Port on 10.5" Question

  1. #11
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    Quote Originally Posted by The Archangel View Post
    Two Live.

    F2S: I am using a F/A LMT BCG with a HD Wolff extractor spring (no O-Ring). The BCG is fairly new with less than 1000 rounds through it.

    GotM4: The upper is not a LMT. It is a Colt cut down to 10.5" and the gas port is opened up to 1/16ths.
    If it is a 2-live double-feed my advice is irrelevant to your problem.
    In my relatively small experience with 10.5 guns I found that heavier buffers and upgraded action springs reduced bounce. That's about all the advice I can give if everything else is in order.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  2. #12
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    Quote Originally Posted by The Archangel View Post
    Two Live.

    F2S: I am using a F/A LMT BCG with a HD Wolff extractor spring (no O-Ring). The BCG is fairly new with less than 1000 rounds through it.

    GotM4: The upper is not a LMT. It is a Colt cut down to 10.5" and the gas port is opened up to 1/16ths.
    Make of the barrel doesn't matter, your gas port is too small.

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

  3. #13
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    The 1/16th drill would not have opened up the port any. Are you sure that is the port that is in it?

    If the port is too small there would not be more recoil...

    9mm buffers should be used in a 9mm. They are heavy but do not "buffer" as well, better to stick to the H's for 5.56.

  4. #14
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    I may be mistaken because the gunsmith that cut down the barrel said a lot of things. I was in awe of the whole process as I am more of an end user and an amateur tinkerer of parts than a machinist. I can build a gun from the ground up with parts that are already made. As far as machining parts, that is beyond my mechanical abilities.

    I thought he said that it was 1/16th, but it may be bigger than that. All I know is that the gas port is significantly larger after he drilled it over stock.
    Last edited by The Archangel; 03-15-09 at 16:04.
    "I stayed at a Holiday Inn Express last night..."

  5. #15
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    Quote Originally Posted by The Archangel View Post
    I may be mistaken because the gunsmith that cut down the barrel said a lot of things. I was in awe of the whole process as I am more of an end user and an amateur tinkerer of parts than a machinist. I can build a gun from the ground up with parts that are already made. As far as machining parts, that is beyond my mechanical abilities.

    I thought he said that it was 1/16th, but it may be bigger than that. All I know is that the gas port is significantly larger after he drilled it over stock.
    Did you let this smith know that you were planning on shooting suppressed most of the time?

    How many rounds through the barrel before it was cut down and port opened?

  6. #16
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    Quote Originally Posted by The Archangel View Post
    I just had a barrel cut down to 10.5" and the gas port opened up to 1/16ths. The recoil is substantially more pronounced now and I am concern of excessive wear (especially when I use a can as it produces even more back pressure).

    I am currently using a standard carbine buffer, but I'm considering switching it out to a 9mm buffer to compensate for the weapon being overgassed. Would that be too heavy for my application? Reliability is my main priority.

    BCG is LMT FA.
    Question, did you try and shoot the gun with barrel at the factory gas port size?

    I see you have a can on the weapon. Remember that a can GREATLY increases pressue (aka felt recoil).

    So let's make the assumption that the weapon is over gassed. Here are some ways to slow things down and get rid of the extra gas:

    1. Use a quality CS buffer spring (like ISMI Tactical Spring Co).
    2. Use at least an H buffer and should really look at H2 and H3 buffers
    3. Use an LMT Enhanced carrier (NOT the enhanced BCG).


    C4
    Last edited by C4IGrant; 03-15-09 at 17:27.

  7. #17
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    What about pulling the gas tube and the FSB and seeing what the gas port hole size is first?

  8. #18
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    Quote Originally Posted by LonghunterCO View Post
    What about pulling the gas tube and the FSB and seeing what the gas port hole size is first?
    This is of course the best thing to do.


    C4

  9. #19
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    Quote Originally Posted by gotm4 View Post
    A factory 10.5" LMT is .071" and runs fine with a CAR buffer. He doesn't have an overgassed problem.
    Robb, LMT told me to run an H? Also I recall that at some point in time they changed the port size to be more forgiving with commercial ammo? It might have been Randall Rausch that posted that I don't know.
    "So have your buddy get a box of stray cats and try to get a good sight picture while he is throwing the cats at you... naked." - KLD

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  10. #20
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    Quote Originally Posted by JLM View Post
    Robb, LMT told me to run an H? Also I recall that at some point in time they changed the port size to be more forgiving with commercial ammo? It might have been Randall Rausch that posted that I don't know.
    If using 5.56mm NATO pressure ammo you should use an H. If only .223 Rem (what most people are using) you can use a CAR or H.
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

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