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Thread: Can I use a non KAC bolt carrier in my Sr-15?

  1. #31
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    Quote Originally Posted by GS5414 View Post
    What you are feeling is likely the difference in KAC gas ports from their earlier guns to the newer ones.

    The older ones were about .078", and the newer somewhere around .082".

    KAC is a smart bunch, and optimized the ports for the ammunition people were generally shooting. Keep in mind, the gun was originally designed for full power/pressure military ammunition, not the normal 55gr blasting fodder many folks use.

    The answer you seek is not necessarily to change the carrier, but to select your ammunition wisely and optimize the gas port diameter, gas tube length (intermediate as a constant in this case), etc. for that ammo. This may mean a different barrel.
    This is correct to a degree.
    Older guns were optimized for M855 and the like.
    We got a lot of complaints about short-stroking, so the port size was opened.
    When we brought the Mod 2 to market, we decided to maintain functionality with lower powered commercial ammunition such as PMC 55gr.
    Port location was changed, so port diameter was also tweaked to provide wide ammo type compatibility.

    I am kind of kicking myself in the posterior for not recommending an HH (2H) buffer in place of the standard SR-15 buffer included with the commercial Mod 2.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  2. #32
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    Though I had to change the carrier on my early SR15 E3 upper for some ammo, I like the pork sizing.

    I only had to change the carrier for crap ammo I used for high volume classes. I love the way it shoots 5.56 stuff.

  3. #33
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    Quote Originally Posted by Failure2Stop View Post
    This is correct to a degree.
    Older guns were optimized for M855 and the like.
    We got a lot of complaints about short-stroking, so the port size was opened.
    When we brought the Mod 2 to market, we decided to maintain functionality with lower powered commercial ammunition such as PMC 55gr.
    Port location was changed, so port diameter was also tweaked to provide wide ammo type compatibility.

    I am kind of kicking myself in the posterior for not recommending an HH (2H) buffer in place of the standard SR-15 buffer included with the commercial Mod 2.
    I've been running H2s in my Mod 1s and they aren't anywhere close to being too heavy. These things are gassers.

  4. #34
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    What do you mean by "gassers"?
    Quote Originally Posted by samuse View Post
    I've been running H2s in my Mod 1s and they aren't anywhere close to being too heavy. These things are gassers.
    I haven't run the 3.0 ounce carbine buffers in SR-15s since the porting changed on the early ones. I do use H1-H3 buffers in some, but most are A5 based now.

  5. #35
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    Quote Originally Posted by tom12.7 View Post
    What do you mean by "gassers"?

    I haven't run the 3.0 ounce carbine buffers in SR-15s since the porting changed on the early ones. I do use H1-H3 buffers in some, but most are A5 based now.
    Gasser as in it has a big ass port and flings brass out about 1-2:00 unless I use an H2 to tame it down. A stock 6921 is softer shooting than my Mod1.

  6. #36
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    What buffer in the 6921? I'm really not looking for ejection direction in this context, too many variables. An H2 does trend to be more rifle action like than the 3.0 carbine action system.

  7. #37
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    Quote Originally Posted by Failure2Stop View Post
    This is correct to a degree.
    Older guns were optimized for M855 and the like.
    We got a lot of complaints about short-stroking, so the port size was opened.
    When we brought the Mod 2 to market, we decided to maintain functionality with lower powered commercial ammunition such as PMC 55gr.
    Port location was changed, so port diameter was also tweaked to provide wide ammo type compatibility.

    I am kind of kicking myself in the posterior for not recommending an HH (2H) buffer in place of the standard SR-15 buffer included with the commercial Mod 2.
    Of course, I didn't want to call out M855 specifically, as there's 62gr stuff out there that looks like A059 but ain't.

    An in-line production change of shipping an H2 buffer with the guns would help a touch, but I wouldn't beat yourself up over it.

    The older SR15s I handled had a second recoil impulse and slower carrier speed that was softer and slower than most current guns that require obnoxious brakes to tune things down.

    Out of curiosity, Jack, if someone were to request an original port size, could it be done?

    S/F

  8. #38
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    Quote Originally Posted by tom12.7 View Post
    What buffer in the 6921? I'm really not looking for ejection direction in this context, too many variables. An H2 does trend to be more rifle action like than the 3.0 carbine action system.
    H2. I pretty much have used stock springs and H2 buffers in everything from 10.3" -20" Colts and everything in between to include BCM mids which are generously gassed these days as well.

  9. #39
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    The H2 idea isn't new, but I would not like to be at the table as the guy who tries to defend the H2 function over a properly massed rifle like or A5 based action system.
    The changes in timing are not always direct between the carbine and rifle action system. Many events occur during cycling, reducing net negatives has always been a priority.

  10. #40
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    Quote Originally Posted by samuse View Post
    Gasser as in it has a big ass port and flings brass out about 1-2:00 unless I use an H2 to tame it down. A stock 6921 is softer shooting than my Mod1.
    My experience has not been the same. In fact, I have not heard of this until you spoke of it.

    May I ask why you are a proponent of the SR-15?

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