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Thread: Barrel thread strength

  1. #1

    Barrel thread strength

    Hi there folks,

    As the title suggests, how must stick can the barrel take without being damaged when using a moderator.

    On a recent shooting trip the heavy window of a European style high seat slammed shut after I'd fired. The wooden window/flap landed on my sound mod with quite a whack that it's left a shiny line/scratch horizontally across it. The mod isn't dented at all but I am concerned about having bent the tip of the barrel, could this happen?



  2. #2
    Very unlikely in the situation you describe, the barrel is stronger than your moderator as it is in effect a thick walled tube, to bend that short section of thread would take enormous forces.
    (The Unspeakable In Pursuit Of The Uneatable.) " If I can help, I will help!." Former S.A.C.S. member!

  3. #3
    I've been told that a whack on the mod can distort the screw threading, so could result in future shots clipping the inside of the mod.
    No first hand experience of this though.

  4. #4
    I can understand your concern it all depends 1) what is bore/ calibre of the barrel eg: 308win cal = 7.62mm
    2)the thread size of the moderator/barrel eg 1/2"unf =12.7mm-7.62=5.08Divide by 2+=2.54 wall thickness each sidewall so no not a lot of metal left and a hard blow could "bend" or fracture the end of the barrel especially if there is no radius at the barrel shoulder /thread start.

  5. #5
    As per Roebuck9 I think your concern is wholly understandable.

    I've always thought the length of 1/2" UNF thread given to 22 rimfires is far too short and is why I have mine cut to 30mm.

    At the risk of stating the obvious it is the significant additional leverage a moderator may impart to a barrel if dropped or fallen upon that can ensure more than a temporary change in zero.


  6. #6
    Thanks for the replies folks! The gun is a Sako A7 s, in 308 and the thread is 14x1. I'll be so annoyed if it is damaged because the gun is only 3 months old!!

  7. #7
    308 is very tolerant of barrel length so having the end lopped off and rethreaded is not then end of the world. Try it first though.

  8. #8
    if it has just slammed on the mod I can't see a huge lever involved so the mod should have taken the brunt

    if however the barrel was positioned so the fulcrum was much closer to you and the force was applied to the end of the mod I can see how it may damage the barrel

    just pull the bolt and look through with and without the mod
    depending on bore size the tolerance is quite tight and you can easily see potential interference

    inspect the thread for damage otherwise

  9. #9
    The biggest danger is if the thread is bent, the bore may no longer be in concentric alignment with the moderator. Don't shoot it till it has been checked.
    Look up the bore to see if you can see the moderator offset. You certainly don't want bullets hitting the inside of the moderator.
    You can easily see if a moderator is out of line by laying a long (longer is better)ruler along the outside & back along the barrel, Measure the gap down to the barrel from the ruler. Do this at multiple positions around the moderator - errors will soon become evident. This method does rely on the moderator being concentric of course.
    Another way to check is to put a close fitting rod in the barrel bore with the moderator in place. Again any excentricity will show itself.


  10. #10
    So the thread is 14x1, shearing force required for a 14mm bolt, as opposed to a tube section, 20 tonnes approx.
    (The Unspeakable In Pursuit Of The Uneatable.) " If I can help, I will help!." Former S.A.C.S. member!

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