338 muzzle brake exit hole diameter

Discussion in 'Gunsmithing' started by kiongozi, Aug 25, 2011.

  1. kiongozi

    kiongozi New Member

    Messages:
    3
    Joined:
    Aug 25, 2011
    I have a new Weatherby Accubrake for a number 2 coutour barrel and am wanting to install it on a Vanguard re-chambered from .338 Win Mag to .340 Weatherby.

    I have figured the thread to b 9/16" - 24 t.p.i, what puzzles me however is the exit hole through the centre.

    I measure the hole as it comes new at .395", that is a good .055" above bullet diameter .

    Is there an optimum clearance size for a muzzle brake any given calibre and in particular for a.338 bore?

    I make the assumption that the lesser the clearance the more effective the brake will be, from my reading of Weatherby's web site it may be that they used one size of brake to fit the .340 - .378 bore rifles as they appear to only offer 4 sizes of brake for the entire Wby calibre range.

    Whilst I have no doubt the brake will work to some degree am I wasting my time screw cutting the barrel to fit this particular brake to a .338"

    many thanks

    Jonathan

    BTW

    I am not totally new to LRH, my old password and user account/e-mail address were on my office computer which I no longer have access to so am now resorting to my home PC as it proved quicker to re-register a new.
     
  2. M67

    M67 Well-Known Member

    Messages:
    52
    Joined:
    Aug 12, 2010
    My gunsmith just made one for me, I measure the exit hole as .382" - 9.7mm.
    I havent shot it yet (as a certain Canadian stock maker seems to have gone into slow mode), but i see both my 6.5mm and .300 brakes measure the same 1mm - 0.04" above bullet diameter, and both rifles shoot extremely well.

    K
     

  3. chrishatley

    chrishatley Well-Known Member

    Messages:
    101
    Joined:
    Feb 22, 2011
    From what I understand, the exit hole in the brake should be .020" over bore diameter. Hope this helps.
     
  4. J E Custom

    J E Custom Well-Known Member

    Messages:
    7,270
    Joined:
    Jul 29, 2004
    +1

    .015 is minimum and only if it is installed with a Lathe for accuracy and a boring bar is used
    to open the hole. but .020 is recomended.

    So the hole dia. for a 338 should be .358 to .360.

    Any more is not nessary as long as it is installed properly.and reduces the effectiveness of
    the brake.

    This is a precision installation and should not be done by hand under any circumstance.

    J E CUSTOM
     
  5. FEENIX

    FEENIX Well-Known Member

    Messages:
    9,806
    Joined:
    Dec 20, 2008
    C&P

    (Adventures With Muzzle Brakes | RVB Precision)
     
  6. Hired Gun

    Hired Gun Well-Known Member

    Messages:
    1,537
    Joined:
    Apr 21, 2003
    That's how Weatherby specs it and it is still quite effective. I took my oversize Accubrake off my 300Wby Accumark and replaced it with a state of the art reverse thrusting baffled brake, fit at .020" over bullet size and the differrence in recoil was zip.
     
  7. J E Custom

    J E Custom Well-Known Member

    Messages:
    7,270
    Joined:
    Jul 29, 2004
    The accubrake is also a very efective baffeled break and it has chambers that also redeuce recoil.
    Weatherby claims their break has aproxamatly a 53% reduction.

    Very few brakes can produce that much reduction if it is true, so it is no surprise that the new break did not do any better.

    Look inside the Accubreak and you will see what I am talking about.

    I like the baffled breaks but use the Accubreak when I can find them.

    J E CUSTOM
     
  8. kiongozi

    kiongozi New Member

    Messages:
    3
    Joined:
    Aug 25, 2011
    Thank you everyone for your kind replies. I guess this is one of the areas where theory and reality do not always correspond. My guess was that the closer the clearance the more effective the brake would be but Weatherby seem to differ in practice.

    I will run with the accubrake for now and if it proves ineffective with a .055" clearance will re think matters.

    Best

    Jonathan