barrel diameters and muzzle brakes.

Discussion in 'Gunsmithing' started by J E Custom, May 9, 2014.

  1. J E Custom

    J E Custom Well-Known Member

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    There seems to be a lot of varying opinions on what size of barrel can or can't have a muzzle brake installed.

    I am sure some will disagree and that's all right, so hear goes.

    After talking to barrel makers and engineers and using there recommendations for MINIMUM wall thickness I found that this was a rule that most were not willing to brake for safety reasons.

    After doing all of the calculations using this information this is what I came up with and use for all of my brake installations.

    It is based on the caliber of the barrel and safe wall thickness remaining after threading. these dimensions at the muzzle of the barrel are "MINIMUM" for safely installing a muzzle brake.

    .224 bore = .563 muzzle diameter
    .244 bore = .584 muzzle diameter
    .257 bore = .597 muzzle diameter
    .264 bore = .604 muzzle diameter
    .277 bore = .617 muzzle diameter
    .284 bore = .624 muzzle diameter
    .308 bore = .648 muzzle diameter
    .323 bore = .663 muzzle diameter
    .338 bore = .678 muzzle diameter
    .350 bore = .690 muzzle diameter
    .375 bore = .715 muzzle diameter
    .400 bore = .740 muzzle diameter
    .416 bore = .756 muzzle diameter
    .425 bore = .765 muzzle diameter
    .458 bore = .798 muzzle diameter
    .470 bore = .810 muzzle diameter
    .510 bore = .850 muzzle diameter
    .570 bore = .910 muzzle diameter
    .600 bore = .940 muzzle diameter

    These dimensions are also minimum recommended wall thickness after fluting (Bottom of flute to bore).

    There is some support from the muzzle brake depending on the quality of the threads, but I don't recommend relying on the brake to make up the minimum wall thickness. on very small barrels finer thread pitches are normally used because on thread height (The finer the thread the shorter the thread height, using less of the barrel wall thickness.

    Also, as bore diameters increase more stress is placed on the barrel because of the larger surface
    of the barrel wall.

    This post is not intended to be the last word, it is just a guide line to help decide if it is possible to install a muzzle brake safely on your barrel.

    Be safe

    J E CUSTOM
     
  2. drbill

    drbill Well-Known Member

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    Good info. Thank you.
     

  3. FEENIX

    FEENIX Well-Known Member

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    This is another excellent info and should be on the "sticky".
     
  4. 308 nate

    308 nate Well-Known Member

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    J E Custom . I am confused by your post as you do not address thread tenon diameter.are you saying that a 1/2 and 9/16 inch thread should never be used?It looks like your listing minimum muzzle diameter ,are you also saying that this would be your minimum minor thread pitch diameter? in fact 5/8x24 minor pitch diameter is .575 there for anything over.224 bullet diameter would be out.Could you clarify are you saying that you can install muzzle brakes on these diameter barrels, or are these dimensions referring to minor thread pitch diameter.if not what is the minimum thread diameter for caliber?
    308nate.
     
  5. matemike

    matemike Well-Known Member

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    Thanks Jerry. Excellent info.

    It's comforting to know you look after these things especially since I dropped off my weatherby earlier this week for bedding and one of your incredible assassin muzzle brakes.
     
  6. J E Custom

    J E Custom Well-Known Member

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    Yes you can use 1/2'' and 9/16" threads for brakes.

    Example = If you have a .224 (223) you would need a .550 barrel diameter to install a 1/2'' 28
    break. the minimum I listed was .563 to allow for poor threads or fit.

    I use the Minor thread diameter because that is the actual wall thickness to the bore.

    The number that engineers gave me was .140 thousandths absolute minimum wall thickness
    for fluting at, or near the muzzle and muzzle brake threads Minor thread diameter should not be less.

    If you do the numbers, most ARs are marginal with a 1/2x28 TPI thread. .224 bore diameter from
    .4768 Minor thread diameter = .2528 divided by 2 you end up with a wall thickness of .1264,you end up with .013 thousandths less than the recomended .140.

    This is the case where they are relying on the brake for some support .

    The chart I use, takes in to account for as much as can be useful and allows for a fairly safe installation as long as the thread fit is very good.

    The size of the thread and pitch is determined after the wall thickness is determined.

    All Good questions , And I hope I answered them.

    Remember these are my suggestions and if someone wants to deviate from It, That's fine.

    J E CUSTOM
     
  7. J E Custom

    J E Custom Well-Known Member

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    Thanks !

    I have some rules of my own and If I don't feel it is safe or the correct way to do it I simply decline

    Just because others do something that may be safe, I have to be convinced before I will do it. It does not mean that they are doing anything wrong, I just want to be careful.

    Firearms are not forgiving and it only takes one mistake.

    J E CUSTOM
     
  8. 308 nate

    308 nate Well-Known Member

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    Okay so here's what I am understanding.the minimum muzzle diameters is referring to Minor thread diameter.I will list UNR minor diameter Max Ref A3.
    1/2x28tpi= .4574 so .140×2=280+bullet diameter.224= .504
    9/16x24tpi =.5129 so this would work for.224.and .243 of your willing to cross the line.
    5/8x24tpi =.5754 so .140×2=280+bullet diameter .308=.588 so .338 would be out of the question.My question then is this a line not to be crossed.I have talked to many barrel manufacturers as well and they recommend .15 minimum wall thickness on stainless, which I do follow for fluting .I would be interested to hear what your minimum thread diameter and pitch per caliber would be for stainless steel and chrome moly,and if you treat them differently?please forgive all of my questioning. I am just trying to understand what you're saying. I have literally put hundred of breaks on 30 caliber barrels with 1/2x28tpi with zero problems. in fact in the early days I even threaded a few .338 barrels 1/2×28tpi with no problem, although this does not meet my current guidelines. All the best .308Nate
     
  9. CliffM

    CliffM Well-Known Member

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    Is there a muzzle pressure that the minimum wall thickness is based on.

    Out of curiosity I compared my 6.5 Sherman loads to 6.5x47 loads with different barrel lengths and powder burn rates. the calculated results spanned from 7000-17000psi at the muzzle, that is quite a large range IMO to arrive at a generic safe diameter per caliber.

    Cliff
     
  10. J E Custom

    J E Custom Well-Known Member

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    Thanks Nate, your Questions are good.

    The Engineers are using .140 as a safe wall thickness based on what I have been told.

    I actually use a minimum wall thickness of .150 on all of the calculations regardless of barrel material. .010 thousandths is not very much more but it is more.

    Different thread pitches have different thread major and minor diameters and I try to select the largest thread diameter above the minimum wall that will exceed the minimum requirements.

    In other words, if I can use a 5/8x24 thread on a .224 barrel as long as I have enough shoulder to seat/time the brake even though I could use a 1/2x28 I do.

    I have seen muzzle brakes that were shot off the barrel (For many reasons) that took the tenon with them. In every case it was ether the tenon thread was to small, the brake was to thin, or the threads were poorly done and in some cases the bullet was striking the brake and took the brake with it.

    I see lots of big bore rifles that have no provisions for a muzzle brake because the barrel is to light
    to thread so I don't.

    I consider myself fearless and the thought of placing a brake on a .338 using a 1/2x28 thread pitch scares the hell out of me. I am glad that you have not had a problem with the 30s and the 338s with such a thin barrel wall (The .308s would have a .074 thousandths wall thickness and the .338 would have a.059 wall thickness) making the .308 1/2 the recommended wall thickness and the
    .338 1/3rd of the recommended minimum wall thickness. and if that doesn't scare you I would not want to piss you off.

    This is truly a case of more is better but IMO less is unsafe and should never be used.

    And yes I do draw the line at .150+ wall thickness and if the barrel is above this minimum I will use the largest threads possible to increase the wall thickness.

    The numbers on the chart are a little conservative (+ .010 )but not so much as to make it difficult to do the job. It is intended to be a guide line to answer the question for someone that doesn't have a machinist or gun smith background that may be thinking about installing a brake on a light contour barreled rifle.

    Thanks again for your questions and I hope I answered them to your satisfaction

    J E CUSTOM
     
  11. 308 nate

    308 nate Well-Known Member

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    I would assume it would be for 65000 psi.I also believe there is a generous safety margin figured in.if I get some time I will run the actual numbers on this for specific alloys commonly used for barrel.
     
  12. 308 nate

    308 nate Well-Known Member

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    I guess the Vais brakes are out of the question then. As there 30 caliber brake has a 1/2x32tpi and there .338 brakes have a 9/16x32.I have never seen a threaded brake, come off a barrel thankfully.My computer says we're over 400 brake installs recorded.all the best .
    308Nate
     
    Last edited: May 10, 2014
  13. J E Custom

    J E Custom Well-Known Member

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    Last Comment.

    This has nothing to do with the brand or type of brake used It is about the Wall thickness of the barrel after threading.

    I personally have not installed 400 brakes (Around 250) and if someone wants to use something
    that is below the recommended barrel wall thickness, that is there choice NOT MINE.

    The chart that I provided will keep a person within these recommended safety limits.

    J E CUSTOM
     
  14. J E Custom

    J E Custom Well-Known Member

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    Sorry I missed your post.
    The engineers I talked to said it was based on 15,000 psi. the average is 10,000 psi but it may see
    more so the include a safety factor.

    As long as it is based on 15.000 psi they consider it safe.

    J E CUSTOM