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  1. #1
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    Default AR15 gas port size for a 10.5"?

    How big should the gas port be made for a 10.5" to fire all ammunition reliably?

    Is there a magic number?

    I saw a Compass Lake barrel ported to .07. Spikes reports range between .073-.089 and ADCO says what ever size is desired.

    Any reccomendations?

  2. #2
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    Default Re: AR15 gas port size for a 10.5"?

    no larger than .093 I think.

    the reason why the 10.5s arent all that reliable is the lack of dwell time between the port and the muzzle... you have to use a larger gas port to make up with the faster gas pressure drop, but no so large as to provide too powerful of a gas pulse, that can cause accelerated wear on the receiver, and too fast ejection leading to ripped case heads, etc.

    also, the buffer selection is a big choice, colt used a 2 piece mechanical heavy buffer for the 10.5" barrel to prevent bolt bounce.

    so go up cautiously, and dont forget the other factors like buffer, extractor, chamber type and ammo.
    "Oderint Dum Metuant" - BMFH

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  3. #3
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    Default Re: AR15 gas port size for a 10.5"?

    Quote Originally Posted by JayBell View Post
    no larger than .093 I think.

    the reason why the 10.5s arent all that reliable is the lack of dwell time between the port and the muzzle... you have to use a larger gas port to make up with the faster gas pressure drop, but no so large as to provide too powerful of a gas pulse, that can cause accelerated wear on the receiver, and too fast ejection leading to ripped case heads, etc.

    also, the buffer selection is a big choice, colt used a 2 piece mechanical heavy buffer for the 10.5" barrel to prevent bolt bounce.

    so go up cautiously, and dont forget the other factors like buffer, extractor, chamber type and ammo.
    I was told that Colt uses .093, and they tend to over gas their firearms to allow ability to shoot various kinds of ammo. Which is what I am looking for. I hope to be able to shoot low power .223 and standard 5.56. I figured I could compensate for the over gas by H# buffer and stiffer springs.

    I just wanted to see if there was a "standard" since I am seeing a lot of different sizes out there. I was considering going with .089.
    Last edited by FJR86; July 28th, 2010 at 12:04 AM.

  4. #4
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    Default Re: AR15 gas port size for a 10.5"?

    Quote Originally Posted by FJR86 View Post
    I was told that Colt uses .093, and they tend to over gas their firearms to allow ability to shoot various kinds of ammo. Which is what I am looking for. I hope to be able to shoot low power .223 and standard 5.56. I figured I could compensate for the over gas by H# buffer and stiffer springs.

    I just wanted to see if there was a "standard" since I am seeing a lot of different sizes out there. I was considering going with .089.
    frankly, i'd go smaller the better, and work up for good operation... testing at the range, i usually had a clamp on gas block, a battery drill, and a series of drills to get it right on the 7.5-10.5" barrels.

    problem with going to increasingly heavy buffers and stiff springs is that you then increase the velocity of the closing bolt, again maybe causing carrier bounce, etc.

    in my m16 with the 7.5 and up barrels, i use a standard carbine spring, the the DPMS copy of the colt commando 2 piece mechanical buffer.

    it runs flawlessly on my 6.5", 11.5" and 14.5" barrels. I have to swap the buffer to get my 20" Diemaco/Colt LMG upper to run.
    "Oderint Dum Metuant" - BMFH

    "Tact is for people not witty enough to use sarcasm"

    Note: any whingeing crazy that hits my PM inbox will be deleted without reply

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