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Thread: 16" intermediate gas, gas port sizes. My SR15 is undergassed, lets talk ideal sizes.

  1. #11
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    The gun uses the sr15 marked carbine buffer and colt carbine spring and I've tried a white sprinco spring.

    The bulb on the end of the gas tube is non existent. When I run my nail over it its like it was never there, just a smooth polish all the way to the end. I am going to replace the gas tube and see what happens. At 57$ on operation parts its definitely F-U expensive, but thats the pleasure of KAC ownership I guess...

    I'm still interested if the .078" it measures at is considered too small for the gas system length?
    Last edited by TMS951; 01-09-19 at 14:12.

  2. #12
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    Quote Originally Posted by TMS951 View Post
    The gun uses the sr15 marked carbine buffer and colt carbine spring and I've tried a white sprinco spring.

    The bulb on the end of the gas tube is no existent. When I run my nail over it its like it was never there, just a smooth polish all the way to the end. I am going to replace the gas tube and see what happens. At 57$ on operation parts its definitely F-U expensive, but thats the pleasure of KAC ownership I guess...

    I'm still interested if the .078" it measures at is considered too small for the gas system length?
    I've heard of that happening with gas tubes before.

  3. #13
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    Quote Originally Posted by TMS951 View Post
    The gun uses the sr15 marked carbine buffer and colt carbine spring and I've tried a white sprinco spring.

    The bulb on the end of the gas tube is no existent. When I run my nail over it its like it was never there, just a smooth polish all the way to the end. I am going to replace the gas tube and see what happens. At 57$ on operation parts its definitely F-U expensive, but thats the pleasure of KAC ownership I guess...

    I'm still interested if the .078" it measures at is considered too small for the gas system length?
    ETA: disregard, this is in regard to KAC's intermediate spec.
    Last edited by pointblank4445; 01-09-19 at 12:57.

  4. #14
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    Quote Originally Posted by taekwondopreacher View Post
    I've heard of that happening with gas tubes before.
    There was a recent thread where it ended up being the issue. Had I not recently read that thread I never would have guessed. I've been chasing it for years, I realize its probably slowly been getting worse which makes sense.

    The other thing that now clicks is when I went and swapped rails on it the other day I noticed how dirty the gas tube was from where it goes in the BCG and then forward about 6-7". At that time I thought maybe the tube had ruptured and that was my issue, I cleaned it up and found no splits in it. I now realize it was so dirty because gas was shooting forward out of the gas key due to the loose seal from the gas tube.

    I don't know the round count on this upper. I have a 3k-7k rounds through it, I really don't keep track. When I took it in trade it was very clean and looked good, but round count is unknown to me. The only thing I think to attribute the ware to is one place I take training classes is all fine sand. A lot gets in the action in Vtac classes I took there, actually sand goes everywhere and in everything. I eventually stopped taking classes there because of the sand.

    Due to the ware on the gas tube I am going to install a KAC bolt repair kit I have at the same time to freshen the whole thing up.

  5. #15
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    For future reference, can you measure the diameter of the bulb and report back?

    Quote Originally Posted by TMS951 View Post

    The bulb on the end of the gas tube is non existent. When I run my nail over it its like it was never there, just a smooth polish all the way to the end. I am going to replace the gas tube and see what happens. At 57$ on operation parts its definitely F-U expensive, but thats the pleasure of KAC ownership I guess...
    Black River Tactical
    BRT OPTIMUM Barrels - 16" MPR, 11.5" CQB, 9" PDW
    BRT OPTIMUM-S Barrel - 11.5" CQB Suppressor Gas Drive
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT and PDW Lengths
    BRT EZTUNE Gas Tubes - CAR and MID
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

  6. #16
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    Quote Originally Posted by Clint View Post
    For future reference, can you measure the diameter of the bulb and report back?
    Yes. Once I recieve the gas tube Iíll take the rail and gas tube off, measure both gas tube ends and photograph them side by side. Iíll also photograph any barrel markings while itís apart as well.

  7. #17
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    I'm wondering if the aftermarket gas block is misaligned. I would have someone with a bore scope check it. It is how I check for port alignment.

    As far as the gas tube goes, brownells sells a gauge made by Mark Brown to measure the flared portion of the gas tube while it's still in the upper. It will find wear on the half that's not visible. It's a good gauge.

  8. #18
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    Quote Originally Posted by Failure2Stop View Post
    Can you better define exactly what barrel you have?
    Pics will help.

    On the progress through the legacy, Mod 0, Mod 1, and Mod 2 guns there have been pretty significant changes to the system.
    Wasn't there something too, from KAC, about not running M193 spec ammo? I'll see if I can find it.

  9. #19
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    I think it is time to part out this upper, sell off the questionable parts and buy new.
    "Not every thing on Earth requires an aftermarket upgrade." demigod/markm

  10. #20
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    Quote Originally Posted by Caduceus View Post
    Wasn't there something too, from KAC, about not running M193 spec ammo? I'll see if I can find it.
    IIRC the original SR-15 Mod 0's were ported to run 5.56 pressure ammo exclusively. Of course, buyers complained that Brand X,Y, and Z .223 ammo wouldn't run, and eventually KAC opened up the gas ports. Not sure if they ever got to the point where they offered different porting upon request like Daniel Defense eventually did for their Mk18s, but the current SR-15 gas block, barrel, and gas tube configuration is totally different than the original.

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