Page 1 of 2 12 LastLast
Results 1 to 20 of 25

Thread: Gas port Sizes

  1. #1
    Join Date
    Jun 2006
    Location
    Florida
    Posts
    355
    Feedback Score
    0

    Gas port Sizes

    Who has the low down on gas ports for different length barrels? My main interest is 10.3 and 11.5 barrels but if you have a chart or list of other lengths that would be great. I have an old barrel I'm having cut down so it needs to be opened up so it will run.

    TIA for the help.
    Sad, that it takes someone else to tell you your life is worth protecting and that you are the one ultimately responsible for it.

  2. #2
    Join Date
    Sep 2006
    Posts
    51
    Feedback Score
    0
    Quote Originally Posted by Boom
    Who has the low down on gas ports for different length barrels? My main interest is 10.3 and 11.5 barrels but if you have a chart or list of other lengths that would be great. I have an old barrel I'm having cut down so it needs to be opened up so it will run.

    TIA for the help.
    14.5" and 16" barrels run .062" IIRC 10.3" and 11.5" are .085" and 12.5" is .074"

  3. #3
    Join Date
    Jun 2006
    Location
    Florida
    Posts
    355
    Feedback Score
    0
    Moose thank you.
    Sad, that it takes someone else to tell you your life is worth protecting and that you are the one ultimately responsible for it.

  4. #4
    Thors ~ Hammer Guest
    Heres a good list. Scroll down about halfway.

    http://groups.msn.com/TheMarylandAR1...tenacefaq.msnw

  5. #5
    Join Date
    Oct 2006
    Location
    Clarksville, TN
    Posts
    25
    Feedback Score
    0
    Quote Originally Posted by Thors ~ Hammer
    Heres a good list. Scroll down about halfway.

    http://groups.msn.com/TheMarylandAR1...tenacefaq.msnw

    I wouldn't use that list. I screwed up two barrels following his recommended port sizes. He's got the ports for a 14.5 inch barrel way too large. .61 - .62 is the perfect size for a 14.5 inch barrel, especially if you're running fullauto. On an 11.5 inch barrel go with .69 IIRC, no larger.
    Μολὼν Λαβέ

    Have gun... will travel.

  6. #6
    Join Date
    Jun 2006
    Location
    NoVA
    Posts
    4,983
    Feedback Score
    11 (100%)
    Bump...

  7. #7
    Join Date
    Jun 2006
    Posts
    144
    Feedback Score
    0
    Where exactly is the gas port located. I am thinking inside of the carrier key.
    Could not find any diagrams with this info.

  8. #8
    Join Date
    Jun 2006
    Location
    NoVA
    Posts
    10,627
    Feedback Score
    16 (100%)
    Factory 10.25" CQBR barrel 1x7 .091"

    My AR15Barrels cutdown 10 7/16" LMT (cut down from a factory 14.5") 1x7 .078"
    FFL/SOT armorer

  9. #9
    Join Date
    Jun 2006
    Location
    USA
    Posts
    305
    Feedback Score
    1 (100%)
    Quote Originally Posted by Colt6920 View Post
    Where exactly is the gas port located. I am thinking inside of the carrier key.
    Could not find any diagrams with this info.

    6920,
    The port is in the barrel under the gas block (or front-sight base) and is what bleeds gas through the gas tube back to the carrier key.
    Aubrey<><

  10. #10
    Join Date
    Aug 2006
    Location
    Southern California
    Posts
    1,092
    Feedback Score
    0
    Quote Originally Posted by gotm4 View Post
    Factory 10.25" CQBR barrel 1x7 .091"

    My AR15Barrels cutdown 10 7/16" LMT (cut down from a factory 14.5") 1x7 .078"
    Which one runs smoother?
    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

  11. #11
    Join Date
    Jun 2006
    Location
    NoVA
    Posts
    10,627
    Feedback Score
    16 (100%)
    Quote Originally Posted by AR15barrels View Post
    Which one runs smoother?
    I'll let you know but I'm sure it's my LMT.

    My buddy is drowning in the Colt koolaid but DAMN that make the gas port HUGE!
    FFL/SOT armorer

  12. #12
    Join Date
    Aug 2006
    Location
    Southern California
    Posts
    1,092
    Feedback Score
    0
    Quote Originally Posted by gotm4 View Post
    I'll let you know but I'm sure it's my LMT.

    My buddy is drowning in the Colt koolaid but DAMN that make the gas port HUGE!
    LMT's 10.5" barrels come 0.071" which is done that way to use with a can.
    If someone is not going to run a can, I usually open them to 0.076"
    With your liking of the heavier buffers, I make yours 0.078"

    If someone was to want to stay with a regular cabine buffer, I would go 0.073" and call it good.
    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

  13. #13
    Join Date
    Jun 2006
    Location
    NoVA
    Posts
    10,627
    Feedback Score
    16 (100%)
    Quote Originally Posted by AR15barrels View Post
    LMT's 10.5" barrels come 0.071" which is done that way to use with a can.
    If someone is not going to run a can, I usually open them to 0.076"
    With your liking of the heavier buffers, I make yours 0.078"

    If someone was to want to stay with a regular cabine buffer, I would go 0.073" and call it good.

    Good info. Thanks.

    I think my buddy is going to run a Colt X buffer in his. Right now he has a H3 but hasn't fired it yet and will be using a SureFire 556K suppressor. No wonder why SAW recommended the X buffer.
    FFL/SOT armorer

  14. #14
    Join Date
    Aug 2006
    Location
    Northern Virginia
    Posts
    56
    Feedback Score
    0
    Gotm4 and I fired our rifles side by side the other night. Mine is the Colt cqbr barrel with the .091 gas port and an H3 buffer, gotm4's LMT has the .078 gas port with an H2 buffer I believe. Side by side, they felt very similar to me. I think gotm4 will agree. It was actually pretty suprising considering the differences in our setups.

    AR15barrels, any idea why Colt chose such a large gas port on their factory cqbr barrel?

    I havn't fired my rifle suppressed yet but will soon. According to Specialized Armament Warehouse, the X buffer is necessary to run my rifle suppressed so the thing won't tear itself apart. I really don't want to go that heavy with the buffer but I also don't want to do any damage to my rifle. Any opinions?
    Team Virginia Arms member
    USPSA Limited B and Production C shooter, IDPA SSP-SS

    formerly known as TacticalShooter

  15. #15
    Join Date
    Jun 2006
    Location
    NoVA
    Posts
    10,627
    Feedback Score
    16 (100%)
    Pat,

    I think they feel similar for a few reasons:

    Your barrel is a heavier profile barrel. (Mine was a factory 14.5" LMT...read light same as a Colt 6921 M4 profile before shortening to 10").

    Your buffer is heavier.(a tad over 1oz heavier, H3 is 5.6oz, H2 is 4.57oz).

    Your suppressor mount/muzzle device works a little like a comp/brake. (My AAC Blackout really doesn't do much, I can even see flash with XM193 and it's timed with 1 port facing downward 6 o'clock. Actually when I changed from the original M4-2000 Mod 07 mount which is like a Phantom I immediately could feel more recoil with the Blackout)

    You were shooting PMC 55gr FMJ. (I was shooting MagTech 55gr FMJ)

    The difference our rails (my KAC RAS2), my FSB, vs. your now lo-pro pinned GB, 9.0 LR, X200 and LMT front sight probably even each other out.


    When we compare them with suppressors we'll use XM193 to eliminate the ammo difference. I have a H3 too so we can see how that changes the feel when compared to my own H2.
    FFL/SOT armorer

  16. #16
    Join Date
    Aug 2006
    Location
    Northern Virginia
    Posts
    56
    Feedback Score
    0
    Robb,

    Agree with everything you said except concerning barrel profile. The Colt cqbr barrel is very light under the handguards. No thicker than yours and perhaps a bit thinner. My barrel is also ever so slightly shorter than yours.

    Not easy for me to admit mine's shorter than yours but what's a brother gonna do?
    Team Virginia Arms member
    USPSA Limited B and Production C shooter, IDPA SSP-SS

    formerly known as TacticalShooter

  17. #17
    Join Date
    Jun 2006
    Location
    NoVA
    Posts
    10,627
    Feedback Score
    16 (100%)
    Quote Originally Posted by TacticalShooter View Post
    Robb,

    Agree with everything you said except concerning barrel profile. The Colt cqbr barrel is very light under the handguards. No thicker than yours and perhaps a bit thinner. My barrel is also ever so slightly shorter than yours.

    Not easy for me to admit mine's shorter than yours but what's a brother gonna do?
    Yeah I'm getting old I don't remember the exact profile.
    But I do remember that your barrel measures 10 1/4" and mine is 10 7/16", not much a difference normally but when you get barrels with that little bit of barrel past the gas port it can be very significant in getting enough gas pressure fast enough to cycle the action reliably but then to not have too much. It's a fine science to get it 'just right', if that even possible. Simply put the 10" guns are going to need close attention to preventative maintenance when compared to say a 16" midlength or a 20" rifle length AR. Everything has a 'service life' and the 10" ARs is shorter than most.
    FFL/SOT armorer

  18. #18
    Join Date
    Aug 2006
    Location
    Southern California
    Posts
    1,092
    Feedback Score
    0
    Quote Originally Posted by gotm4 View Post
    not much a difference normally but when you get barrels with that little bit of barrel past the gas port it can be very significant in getting enough gas pressure fast enough to cycle the action reliably but then to not have too much. It's a fine science to get it 'just right', if that even possible. Simply put the 10" guns are going to need close attention to preventative maintenance when compared to say a 16" midlength or a 20" rifle length AR. Everything has a 'service life' and the 10" ARs is shorter than most.
    Due to larger port sizes required to run with such short dwell times, you really have to keep a watch on port erosion and correct for it by going to heavier and heavier buffers as the port enlarges.

    As barrels get longer, the ports get smaller and dwell time becomes less critical.
    That's why you don't see as much change over the service life of a 14.5" or 16" barrel as you do on shorties that are tuned to run right on the ragged edge of available dwell time.
    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

  19. #19
    Join Date
    Dec 2010
    Location
    Texas
    Posts
    2,544
    Feedback Score
    15 (100%)

    Gas Port Location

    I know this is a necropost, but I didn't want to make a new thread and I think this discussion could add to the sticky.

    Basically I was wondering if someone can tell me exactly what length each gas system is? I've gotten multiple different answers to this question through my research, so I thought I would ask here. I'm really only inerested in carbine and midlength port locations, but for the sake of information, if you know them all, then list em

  20. #20
    Join Date
    Jan 2008
    Location
    AZ-Waging jihad against crappy AR's.
    Posts
    19,109
    Feedback Score
    77 (100%)
    Can you be more specific? Your post doesn't make sense. Are you referring to the sizes?

    Quote Originally Posted by Ironman8 View Post
    I know this is a necropost, but I didn't want to make a new thread and I think this discussion could add to the sticky.

    Basically I was wondering if someone can tell me exactly what length each gas system is? I've gotten multiple different answers to this question through my research, so I thought I would ask here. I'm really only inerested in carbine and midlength port locations, but for the sake of information, if you know them all, then list em





    "A firearm should be considered a fighting weapon first. Any other use should be considered a bonus." -Me

    "If you won't walk out the door with a weapon you fixed, why should someone else be expected to?"-Me

    Click here for Semper Paratus Arms AR15 armorer schedule/locations.

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

    Multiple armorer certifications

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •