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Thread: Sumatra .20 barrel

  1. #1
    REP: WS Airguns

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    Default Sumatra .20 barrel

    Hi all,
    Question to the Sumatra Gurus; are the Sumatra barrels choked both ends?
    I have a 24 inch .20 barrel, when I push a pellet through the bore to check for marks, the pellet comes to a stop 12mm past the TP, then moves forward untill crown end choke.

    I fitted this barrel to a M10 power plant, and accuracy was worse than with a shotgun at 50m. Used JSB 13.73gr, H&N 13.8gr, Beeman 15.89gr, Eun Jin 22.75gr. JSB did better than the rest, but still bad.
    I cleaned up the TP and crown, started lapping the barrel.

    Thanks for info
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  2. #2
    REP: Froggy Custom Silencers

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    Sumatra barrels are not choked, they are lapped and polished from the factory and basically never needs cleaning. Twist rate for the. 22 is 1 in 24... Not sure about the. 20 cal. Slow twist is perfect for long heavy pellets.
    It's my go to replacement barrel.... I have not had a bad one yet.
    Leade is machined very deep... 22.5 mm before rifling starts, 13.5 mm from middle of the transfer port.
    Make sure the pellet is pushed all the way into the rifling in the m10 install, otherwise accuracy will be terrible.
    5 mm carbine at 40m... JSB 13.7 gr...920fps 5 shot groups.
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  3. #3
    REP: WS Airguns

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    I press fitted this delrin sleeve onto the barrel to fit into the breach; can this cause the "tightning" of the bore?

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  4. #4
    REP: Froggy Custom Silencers

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    Nope... The tightness you feel is where the rifling starts... You'll have to cut the barrel... Redo the TP or lengthen bolt probe until the pellet is pushed fully into the rifling. I don't think the m10 bolt will push the pellet far enough forward.
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  5. #5
    REP: WS Airguns

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    Quote Originally Posted by Froggy View Post
    Nope... The tightness you feel is where the rifling starts... You'll have to cut the barrel... Redo the TP or lengthen bolt probe until the pellet is pushed fully into the rifling. I don't think the m10 bolt will push the pellet far enough forward.

    You are 100% correct, thanks Froggy. When shining light from crown side, then I saw where the rifling starts, exactly where pellets gets stuck.
    Will have to "chop & change"
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  6. #6
    Sharp Shooter
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    Did this work out in the end?
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  7. #7
    MRP

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    Interesting to know, would a longer probe not have been a easier fix?
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  8. #8
    REP: WS Airguns

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    Barrel cut up to the rifling on the lathe, tomorrow I will mill the outer and new TP. Then fit to action and test!!! I CARRANT WAIT!!
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  9. #9
    REP: WS Airguns

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    Quote Originally Posted by pcphunter34 View Post
    Interesting to know, would a longer probe not have been a easier fix?

    Cannot do longer probe, then no space to load pellet
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