Bore not concentric with OD of Custom barrel & qualifications

Discussion in 'Gunsmithing' started by blackbrush, Jan 27, 2011.

  1. blackbrush

    blackbrush Well-Known Member

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    After installing a muzzle brake on a specific rifle I ran the whole process over in my head and most of what I recall, I either didn’t understand or appreciate it.

    The bore is quite offset from the OD. What makes it shoddy looking or ugly is the fit is pathetic where barrel meets brake.

    This rifle shoots OK at best…maybe 0.75 MOA at 100 yards, then it wonders out further.

    For those who have experience in purchasing and fitting custom barrels, what are the simple checks you perform that tend to detect conditions that lend poor accuracy performance? Naturally, I am focusing on barrel blanks that have not been machined for fitting.

    What or how many squawks will you compile before you send it back for a replacement?
     
  2. J E Custom

    J E Custom Well-Known Member

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    The very first thing I do before starting a re barrel is to place the barrel between centers on the
    Lathe and indicate it from one end to the other first checking the shank(Breach)end and every
    6" until I reach the muzzle end.NO MATTER WHO's BARREL IT IS.

    I turn the barrel at least 2 revolutions at each location and right down the out of round/concentricity
    of the barrel off the bore.

    Some barrels have huge issues because they have been straightened after drilling and
    contouring even though the bore is straight.

    This condition makes the barrel thicker on one side than the other and as the barrel heats up
    It expands at a different rate from one side to the other.(Common with factory barrels and
    the reason that after a few shots and the barrel warms up the POI or group size changes)>

    I will except .003 to .005 thousandths of "Total Indicated Run out" but no more. I am not smart
    enough to know How much is OK, I just know that perfect is OK for sure, and that the barrels
    that have been replaced (Because they would not shoot) were .010 thousandths Plus.

    I have been told by some barrel makers that .007 to .010 was exceptable (But they make the
    barrels and want to sell all of them),

    After talking to one barrel maker , he said that there is no good reason that a barrel should be
    more than a few thousandths out of concentricity from the bore.

    I have used over 25 of his barrels sense and found "NONE" that were over .002 end to end and
    less than .001 around the bore.

    As I said even after 25+ of his barrels I still check every barrel.

    On the barrels that were under .005 out I turned the OD true to the bore for chambering and
    installing a break on those other brands, and those that were more than .005 went back.

    I even had one guy tell me that no one checked center to center on custom barrels because
    he had never a rejection. Obviously I did not believe him (There are to many good Smiths
    out there).

    Everything must be concentric from the bore in order to have concentric threads and chambers.
    (A must for accuracy) Why blue print an action and then install it on a crooked or out of round
    barrel?

    Maybe some of the other guys will chime in and give there opinion on this.

    I also don't know how much off center the threads and the bore of a break can be
    before it effects accuracy so I cut the threads on the lathe to center and bore the finished
    diameter of the caliber hole+.020 with the brake installed on the barrel still in the thread
    setup stage for concentricity to the bore. I do feel that any off center condition can't be good
    especially if the bullet contacts the break.

    I have My comfort zone and others may have a different opinion but Perfect is still best if
    one can achieve it.

    J E CUSTOM
     
    Last edited: Jan 28, 2011

  3. sinarms

    sinarms Well-Known Member

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    I have worked with many barrels and like JE stated there are some that are very bad. The best I have seen to date have come from Brux, I have 1 .224 1/8 twist barrel from them that was only .0002" off. A lot of the lower end barrels are going to be farther off just because the lack of time and money put into them, if they sell a blank for $100 they can't spend 4hrs finishing it. You get what you pay for in barrels.
     
  4. shortgrass

    shortgrass Well-Known Member

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    I always indicate a barrel in using the bore not the outside. Goes for both ends, tenon for screwing into the receiver, threading for muzzle break. Dial in on the outside to match break to barrel.
     
    Last edited: Jan 28, 2011
  5. blackbrush

    blackbrush Well-Known Member

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    Good point/s. I would presume there are many different barrels (with respect to quality) as there are shooting disciplines. I should have narrowed it down considerably...

    And, yes sir, I bet .007"-.010" may be adequate for say a hunting rifle used in areas where 100 yards or less shots are the norm. I don't know but some smiths may have a tendency to build for their area's uses. (And I am on longrangehunting's website, not that-ought-to-be-about-right.com)

    For long range use that will result in precise accuracy what other "tests" will you insure the barrel meet/exceed?

    Borescope inspection?

    Pushing a lead slug through it?

    How important do you feel conveying the intended use or precision demands to the barrel maker is?

    Is there any "somewhat" consistency in quality control with those that produce accurate precision barrels?
     
  6. Hired Gun

    Hired Gun Well-Known Member

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    I am with Ted on this one. Thread, chamber and crown from the bore centerline 2.5" to 3" on each end and then dial in on the outside when contouring the brake to match the barrel.