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Thread: 12.5" barrel characteristics ??

  1. #1
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    12.5" barrel characteristics ??

    I have run 10.3-11.5" barrels suppressed and non-S for some time, but have fairly recently been trying 12.5. I have noticed what seems to me like a larger difference in operating group speed, and the associated functions, with 12.5 than with the shorter barrels.
    For example, I have a Colt SOCOM I cut down to 12.5" with the factory .063" port. It is at the low end of the functionality range without the can, and at the high end with it. It's very over-gassed.
    For comparison, I have an 11.5" that I have gassed to be reliable with and without a suppressor. With the suppressor, it runs well, but is not as over-gassed as the 12.5.
    I would have thought that the 12.5 would be less sensitive to back pressure changes than the 11.5.

    I'm interested in observations and experiences of others who run 12.5" barrels both suppressed and non-S.
    Last edited by MQ105; 07-02-18 at 19:58.

  2. #2
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    Although I've never suppressed a 12.5, I can tell you that every SBR is it's own animal. My guess is that there's more to it than just barrel length.

    Pappabear and I ported down several SBRs with insertable ports. We shot a bunch of them at the same range trip, and I can tell you that even though all of them showed dramatic performance increases, they all had there own recoil impulses. I've had guns that are more gassy than others for no logical reason. And I've also had a gun that ran perfectly with an adjustable block, but the port snap was so loud it hurt my right ear.

    SBRs just tend to have their own subtle varying characteristics.
    "You people have too much time on your hands." - scottryan

  3. #3
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    Interesting.

    What's the port sizes on the shorter barrels?

    The observed difference could be due to the difference in timing.
    Last edited by Clint; 07-02-18 at 15:38.
    Black River Tactical
    BRT OPTIMUM Barrels - 16" BRT EXT Gas System
    BRT Covert Comps 7.62 + 5.56 + 9mm
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports
    BRT MicroPin Gas Blocks .750" & .625"
    BRT MarkBlue Gas Tubes - BRT EXT and PDW Lengths

  4. #4
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    What gas tube lengths?

    I’m running my triarc 12.5 mid length
    With slr 7 tuned about 11clicks from full off

  5. #5
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    I have a BCM 12.5 Kino and it runs 100% suppressed and unsuppressed. I am certain that markm has shot it at least once or twice.



    Owner/Instructor at Semper Paratus Arms

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  6. #6
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    Quote Originally Posted by Clint View Post
    Interesting.

    What's the port sizes on the shorter barrels?

    The observed difference could be due to the difference in timing.
    Id be more concerned about the design of the can adding too much back pressure. A 0.063" carbine gas port on a 12.5" is very conservative. I like 0.068" for suppressed and unsuppressed use on a 12.5".

  7. #7
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    All barrels have carbine length gas systems.
    -I have a DD 10.75" that was cut down from 14.5. It has a .0625 insert I made. It runs both S and non-S. Griffin M4SDII. (I can't speak highly enough of this suppressor.)
    -Sionics 11.5" with .0650 port, runs well with and without SOCOM RC2. I started with a small port and enlarged until it ran the way I wanted. (Thank you Sionics.)
    -Colt 11.5" heavy profile (FBI) with .0635 insert. Runs well with and without RC2.

    It's quite true that each barrel/gun combo is definitely unique. I like to port mine so they will run without a suppressor (just in case), cold, dirty, and dry. The difference suppressed is notable, but not too bad. This 12.5 borders on violent with the can, yet barely runs without it. It runs 100% thus far, it's just...super snappy. All uppers run with the same lower specs: A5 RE, A5H2, Tubbs SR-25 flat spring. The difference from non-S to S seems much greater than with the shorter barrels.
    Last edited by MQ105; 07-04-18 at 11:37.

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