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Thread: Opened up Gas Port on 10.5" Question

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    Opened up Gas Port on 10.5" Question

    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.

    Last edited by The Archangel; 03-15-09 at 12:52.
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    What ammo do you shoot through it the most? If the ammo is under pressure i would try an H first.

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    Quote Originally Posted by Adam View Post
    What ammo do you shoot through it the most? If the ammo is under pressure i would try an H first.
    I had a limited amount of time on the range so I was only able to put two magazines of M193 through it on rapid fire (mostly controlled pairs). Out of the two mags, I had one double feed.
    "I stayed at a Holiday Inn Express last night..."

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    Did you have a REAL double-feed or did you have an dropped, I.E. interrupted extraction?

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    Quote Originally Posted by Heavy Metal View Post
    Did you have a REAL double-feed or did you have an dropped, I.E. interrupted extraction?
    I'm sorry, I'm not sure what that is. One round was halfway in the chamber. The second round was jammed underneath it. I had to lock the BCG back, remove the magazine to clear the malfunction.
    "I stayed at a Holiday Inn Express last night..."

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    Two live rounds or a live and an empty?

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    I have no idea what "optimal" gas port size is for a 10.5, but your description sounds like a dropped extraction due to over-gassing to me.

    What do you have as far as extractor tensioning? You might need the full BCM upgrade to ensure good extraction. You might also want to replace the ejector spring (depending on how used the bolt is) to mitigate ejection problems that can arise from over-tensioning the extractor.

    Good news is that these are all fairly inexpensive. If your gun is running (not short-stroking) with a 9mm buffer, I see no reason to drop the buffer weight. If anything it will delay the unlocking and extraction a bit, which is a good thing, as I am sure you know. ETA- just saw that you are using a standard CAR buffer, I think that stepping up to an H3 would be a good start, but of your gun is more gassed than "normal" 10.5 guns, a 9mm might be the better solution.
    Last edited by Failure2Stop; 03-15-09 at 14:03.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

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    Isn't a 1/16th bit .0625?

    What is the normal orafice for a 10.5 barrel?

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    Quote Originally Posted by Heavy Metal View Post
    Isn't a 1/16th bit .0625?

    What is the normal orafice for a 10.5 barrel?
    A factory 10.5" LMT is .071" and runs fine with a CAR buffer. He doesn't have an overgassed problem.
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

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    Quote Originally Posted by Heavy Metal View Post
    Two live rounds or a live and an empty?

    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.
    Last edited by The Archangel; 03-15-09 at 14:54.
    "I stayed at a Holiday Inn Express last night..."

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