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Thread: barel threads

  1. #1

    barel threads

    I usually thread barrels for moderators or flash hide, with 1/2 " unf . Is there any reason any rifle upto 308 cal should not have this ?

    cheers

  2. #2
    1/2 thread is more then strong enough it is said. but depending on the barrel thickness a lot of smith like to take the least amount of metal off they can.

    sako have sporter barrels m14x1 and there varmint barrels m18x1

  3. #3
    Quote Originally Posted by jay 22 View Post

    sako have sporter barrels m14x1 and there varmint barrels m18x1
    If Sako use an M14x1-mm on a sporter barrel, I just hope it is a heavier profile than Browning use on X-Bolts.
    My X-Bolt was M14x1-mm on a barrel that was only 15.01-mm diametre, not enough left of the shoulder to hold a moderator square

    Neil.

  4. #4
    I was working on the princaple 1/2" unf is ok for 7.62 bore dia - (12.7mm) 1/2 unf thread leaves over 5mm, 2.5mm in wall thickness either side, with good shoulder, on a 17mm Dia sporter barrel.

    I never got my head around why there was 14x1 unless a huge bore.

  5. #5
    Your maths needs looking at, you seems to have forgotten the depth the thread is cut too.
    Personally I think is a little weak, maybe fine with a reflex type mod that has a bush to add support
    in thecase of a knock, but I would not want to risk it with and end mount can.
    With the 17-mm barrel and 7.62 bore M14x1 is a perfect answer, strong enough and decent shoulder.

    Neil.

  6. #6
    Guy's,

    The thought that Sako are using an M14 is somehow "risky" seems absurd.

    Stan

  7. #7
    1/2x20 unf is not great on 30cal, just too weak.
    thats why on thin 30 cal barrels the 1/2x28 UNEF is prefered.
    edi

  8. #8
    Distinguished Member Ronin's Avatar
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    I really do not like 1/2 UNF threads on .30 cals.


    Thats, REALLY, do not like them.


    Too weak IMHO.


    Bore on a .30 is .308 to the base of grooves.

    Thread OD (outside diameter) = .500"


    .500 - .308 = .192 barrel wall thickness - divided by 2 = .096"


    Now, most 1/2" x 20 TPi threads will have a root depth of circa .060"


    So, the issue:


    .096" barrel wall thickness - (minus) .060" thread root depth


    = .036" barrel wall thickness at root.......


    65000 psi when the powder ignites in the chamber - doesnt instill confidence in me at the muzzle if the barrel wall is so thin....



    Much prefer M14x1 or larger thread diameter - at a push 1/2x28 (1/2" UNEF), but that has only marginally less root depth.....

  9. #9
    Quote Originally Posted by Redmist View Post
    I really do not like 1/2 UNF threads on .30 cals.


    Thats, REALLY, do not like them.


    Too weak IMHO.


    Bore on a .30 is .308 to the base of grooves.

    Thread OD (outside diameter) = .500"


    .500 - .308 = .192 barrel wall thickness - divided by 2 = .096"


    Now, most 1/2" x 20 TPi threads will have a root depth of circa .060"


    So, the issue:


    .096" barrel wall thickness - (minus) .060" thread root depth


    = .036" barrel wall thickness at root.......


    65000 psi when the powder ignites in the chamber - doesnt instill confidence in me at the muzzle if the barrel wall is so thin....



    Much prefer M14x1 or larger thread diameter - at a push 1/2x28 (1/2" UNEF), but that has only marginally less root depth.....

    Although I am in general agreement with you regarding the thread dia compared to bore, I would say it's a little dubious quoting 65kpsi in the chamber then inferring these high pressures at the muzzle..
    A quick calculation gives me a chamber pressure ~ 60kpsi with 6.8kpsi at the muzzle approx 470bar not exactly 'high' pressures compared to run of the mill hydraulics - about the same as old tractor hydraulics.

  10. #10
    Distinguished Member Ronin's Avatar
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    Whilst I dont doubt your calculations..


    If one refers to Vaughns book (Rifle Accuracy Facts)


    (for a 270 Win)


    Chamber pressure is circa 60000 psi

    Muzzle blast (exit) pressure - 11500 psi


    I think I may assume that the internal pressure at the moment the base of the bullet is still within the bore immediately prior to exit, the pressure internally would be significantly higher?


    Very thin wall to have such a high loading - albeit for a milli second....

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