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Thread: Gas system explanation

  1. #1
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    Gas system explanation

    Okay, I'm not trying to beat a dead horse. I've been shooting a little while and I've read a massive amount of information on the carbine gas system and can't seem to get any clarification. Why is a 14.5 barrel best for a carbine? And some people have said that a 14.5 creates more pressure than a 16" carbine.

    What's the story? Is a 14.5 carbine roughly equivalent to a 16" middy as far as pressure, wear and tear, etc?

    Thanks for the replies.

  2. #2
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    IIRC...

    The carbine gas system was developed for the shorter CAR rifles with a ~12? Inch barrel. When the army speced the M4 to have a 14.5" barrel they purposely over dwelled the gas system for more reliable operation with a dirty gun.

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    Actually, 11.5-12.5" is best for a carbine length gas system.

    IIRC, the CAR was developed for the Colt Commando with 11.5" barrel.


    With any given gas system, a longer barrel has more gas drive available.

    "Gas drive" is the area under the pressure curve, PSI x SEC is an appropriate unit.

    Also note that pressure is still useful for several milliseconds after the projectile has left the bore.

    Compared to a 16" MID, a 14.5 CAR has roughly 35% more gas drive available, while a 14.5 MID has roughly 12% less gas drive available.


    As long as plenty of gas drive is available, the gas port size makes the biggest difference in the operation.

    For example, a 16" CAR with a .060" port will run much better than a 16" MID with an .093" port.

    In this case the CAR is properly gassed and the MID is way over gassed.

    Quote Originally Posted by odugrad View Post
    Okay, I'm not trying to beat a dead horse. I've been shooting a little while and I've read a massive amount of information on the carbine gas system and can't seem to get any clarification. Why is a 14.5 barrel best for a carbine? And some people have said that a 14.5 creates more pressure than a 16" carbine.

    What's the story? Is a 14.5 carbine roughly equivalent to a 16" middy as far as pressure, wear and tear, etc?

    Thanks for the replies.
    Last edited by Clint; 11-05-14 at 18:56.
    Black River Tactical
    BRT OPTIMUM HFCL Barrels - Hammer Forged Chrome Lined 11.5", 12.5", 14.5"
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 12.5" MRC, 11.5" CQB, 9" PDW
    BRT EZTUNE Preset Gas Tubes - CAR and MID
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

  4. #4
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    Quote Originally Posted by Clint View Post
    Actually, 11.5-12.5" is best for a carbine length gas system.

    IIRC, the CAR was developed for the Colt Commando with 11.5" barrel.


    With any given gas system, a longer barrel has the most gas drive available.

    "Gas drive" is the area under the pressure curve, PSI x SEC is an appropriate unit.

    Also note that pressure is still useful for several milliseconds after the projectile has left the bore.

    Compared to a 16" MID, a 14.5 CAR has roughly 35% more gas drive available, while a 14.5 MID has roughly 12% less gas drive available.


    As long as plenty of gas drive is available, the gas port size makes the biggest difference in the operation.

    For example, a 16" CAR with a .060" port will run much better than a 16" MID with an .093" port.

    In this case the CAR is properly gassed and the MID is way over gassed.
    Exactly. It's a system.
    "That thing looks about as enjoyable as a bowl of exploding dicks." - Magic_Salad0892

    "The body cannot go where the mind has not already been."

  5. #5
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    Quote Originally Posted by Clint View Post
    Actually, 11.5-12.5" is best for a carbine length gas system.

    IIRC, the CAR was developed for the Colt Commando with 11.5" barrel.


    With any given gas system, a longer barrel has the most gas drive available.

    "Gas drive" is the area under the pressure curve, PSI x SEC is an appropriate unit.

    Also note that pressure is still useful for several milliseconds after the projectile has left the bore.

    Compared to a 16" MID, a 14.5 CAR has roughly 35% more gas drive available, while a 14.5 MID has roughly 12% less gas drive available.


    As long as plenty of gas drive is available, the gas port size makes the biggest difference in the operation.

    For example, a 16" CAR with a .060" port will run much better than a 16" MID with an .093" port.

    In this case the CAR is properly gassed and the MID is way over gassed.
    By an an absolutely amazing coincidence, the 14.5" barrel uses the standard CAR 15 gas tube and mounts the standard M16 bayonet.
    Dave

    INNOVATION IS SELDOM ACCOMPLISHED WITHOUT CONTROVERSY.
    My first rule of a gunfight, thanks to John Farnam's wise advice. "Get away from there!"

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    For some reason I'm just having a hard time wrapping my head around what all this means. How do you know if you have the right size gas port for the barrel? And does the 14.5 car put more wear and tear than a 16 car?

    Thanks for your patience everyone.

  7. #7
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    I am pretty sure that I have posted what are considered correct port sizes IAW the TDP and companies in the industry that know what they are doing.

    Quote Originally Posted by odugrad View Post
    For some reason I'm just having a hard time wrapping my head around what all this means. How do you know if you have the right size gas port for the barrel? And does the 14.5 car put more wear and tear than a 16 car?

    Thanks for your patience everyone.



    Owner/Instructor at Semper Paratus Arms

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  8. #8
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    Don't worry, it's simply sophisticated. :-)


    Getting proper gas ports generally requires sticking to a handful of quality manufacturers, as many of the 2nd tier barrels are over gassed.

    Knowing if it's right involves measuring the size and comparing it to known good numbers.


    All things being equal, the 14.5" will have less gas drive than a 16".

    If the gas ports are properly sized for each barrel, they will have nearly identical gas drive.

    Quote Originally Posted by odugrad View Post
    For some reason I'm just having a hard time wrapping my head around what all this means. How do you know if you have the right size gas port for the barrel? And does the 14.5 car put more wear and tear than a 16 car?

    Thanks for your patience everyone.
    Black River Tactical
    BRT OPTIMUM HFCL Barrels - Hammer Forged Chrome Lined 11.5", 12.5", 14.5"
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 12.5" MRC, 11.5" CQB, 9" PDW
    BRT EZTUNE Preset Gas Tubes - CAR and MID
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

  9. #9
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    It appears that odugrad has read so much on the subject that he is now thoroughly confused. Let's see if I can clarify things.

    His Question: Why is a 14.5" barrel best for a carbine? Answer: The standard bayonet fits.

    His question: How do you know if you have the right size gas port for the barrel? Answer: If it was made by a reputable manufacturer.

    His question: Does a 14.5 car put more wear and tear than a 16 car? Answer: No.

    My personal suggestion to odugrad is not to worry about any of this. However, there are NFA issues with the 14.5. Just buy one that you like and enjoy it!
    Dave

    INNOVATION IS SELDOM ACCOMPLISHED WITHOUT CONTROVERSY.
    My first rule of a gunfight, thanks to John Farnam's wise advice. "Get away from there!"

  10. #10
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    One hitch here. Define "reputable". People think DPMS, Bushmaster, Whogivesaphuck Arms and others are reputable. So that needs to be more defined.


    Quote Originally Posted by spdldr View Post
    It appears that odugrad has read so much on the subject that he is now thoroughly confused. Let's see if I can clarify things.

    His Question: Why is a 14.5" barrel best for a carbine? Answer: The standard bayonet fits.

    His question: How do you know if you have the right size gas port for the barrel? Answer: If it was made by a reputable manufacturer.

    His question: Does a 14.5 car put more wear and tear than a 16 car? Answer: No.

    My personal suggestion to odugrad is not to worry about any of this. However, there are NFA issues with the 14.5. Just buy one that you like and enjoy it!



    Owner/Instructor at Semper Paratus Arms

    Facebook: https://www.facebook.com/SemperParatusArms/

    Semper Paratus Arms AR15 Armorer Course http://www.semperparatusarms.com/cou...-registration/

    M4C Misc. Training and Course Announcements- http://www.m4carbine.net/forumdisplay.php?f=141

    Master Armorer/R&D at SIONICS Weapon Systems- http://sionicsweaponsystems.com

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