barrel runout

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Tikkamike, Jun 2, 2010.

  1. Tikkamike

    Tikkamike Well-Known Member

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    I was just wondering what is the worst barrel run out anyof you have seen on a factory barrel and still shoots good? Remingtons in particular.
     
  2. Mikecr

    Mikecr Well-Known Member

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    How are you defining & measuring barrel runout?
    Is this bore straightness, bore index, barrel straightness, bedded overall straightness?
     

  3. Tikkamike

    Tikkamike Well-Known Member

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    Bore straightness. Sorry I didnt think about all the possible questions I was asking
     
  4. Mikecr

    Mikecr Well-Known Member

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    How are you measuring bore straightness?
     
  5. Fitch

    Fitch Well-Known Member

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    Good question.

    Bores in rifle barrels, even the best ones, are definitely anything but straight regardless of whether the OD surface is straight or not. The bore wanders around the barrel centerline (how does one define a barrel centerline) from end to end. Some barrels have more wander than others. A few minutes with one in a lathe headstock shows that right away. The gun drilling process works remarkably well but the bore still wanders around more than one would expect. This is also true of hammer forged barrels.

    Further, the bore at the two ends of a rifle barrel, throat and crown, are probably pointing in anything but the same direction or even at each other. If one defines the bore centerline as the locus of center points at each point in the bore it would wander around a similarely defined centerline for the bore outside cylinder (or cone in the case of a tapered barrel). Neither centerline is straight, and the two are almost never aligned with each other.

    I don't measure bore straightness exactly, but I do get some inclination about how much they wander around looking through the barrel when it is in the lathe headstock, and when I align it to the headstock. If you align both ends and the bore looks like a jump rope going around, send the barrel back. I haven't had that happen yet but I've seen it happen in a gunsmith friend's lathe.

    I don't want to start a long debate of alignment methods but for purposes of discussing bore straightness it is useful to understand a bit of it. That said, I routinely use Gordy Gritters method of alignment for chambering and crowning because I want the bullet heading with perfect alignment into the centerline of the bore segment at and just beyond the chamber throat. I want the plane of the crown to be perfectly orthogonal with the centerline of the last inch or so of bore at the muzzle. What's inbetween doesn't matter within reason. What Gritters method does is align a short segment of the bore at and just beyond the throat with the lathe headstock in the case of chambering. With that done, I've seen the muzzle making a as much as a .050" inch circle. When I chamber the barrel I set up the headspace to index the barrel up instead of left or right. Gordy shows how to do that in his video which is available from Grizzly. There are other ways to do it, good and great barrels have been made using other methods.

    With the last inch of bore before the muzzle aligned with the headstock I've seen the breech end describing similar circles. Now and then I'll get a barrel that has the bore pretty well aligned with the barrel OD but that's just coincidence, nothing the manufacturer really controls.

    I've heard that Savage straightens barrels, and seen pictures of the rig they use to do it by bending them, but I don't know how they measure them. I'm not convinced that bending a barrel to straighten it is a good idea for thermal stability reasons, I'd rather it was made straight to start with, but it apparently works for them. Savage is pretty good at making production choices that optimize accuracy for a given selling price - but I have pictures that show why sometimes you don't want to look in the bore.

    Fitch