Concentricity:How much ?

Discussion in 'Reloading' started by J E Custom, Feb 8, 2010.

  1. J E Custom

    J E Custom Well-Known Member

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    We all strive for the best quality reloads and this is just another area to deal with.

    My question is- What is an acceptable amount of run out for long range accuracy?

    I would like to end up with no measurable run out but I know/think this is not possible
    and was just wondering what was possible and where the break point was for accuracy.

    I have tested different amounts of run out with the same load and found that it did
    make a difference in both accuracy and SDs. I will post the results but I was wanting
    hear from the membership first.

    I have improved my reloading process from an average run out of .0035 to .0005 and
    cannot seem to get any better results and didn't know if this was about as good as
    I can expect.

    Any comments and /or suggestions would be appreciated.

    Thanks
    J E CUSTOM
     
  2. 300rum

    300rum Well-Known Member

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    for best results i sort the bulets by 1thousant runout.
    best - 0-1th
    acceptable 2-3
    4-5 runout - not recom. for reliable shots past 800yrd.
    if you paid attention to details when reloading, you can get very good at runout less then 2 thousant.
     

  3. Eaglet

    Eaglet Well-Known Member

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    J E,

    +1 to 300rum said.

    With my setup, it helps when sitting the bullets, I bring them down about half way and bring the ram up turn the cartridge 180° and then I sit the bullet all the way down. I kept playing and checking one by one until I was convinced that it helps.
     
  4. Gene

    Gene Well-Known Member

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    For me, this is the most frustrating part of BR reloading. I use a Holland guage, and have trouble getting consistent run outs on loaded round ogives below .003.

    JE - how did you get down to .0005? Are they consistent?

    300rum - How are you doing run outs on bullets alone? I assume you do this prior to seating??

    I believe that run outs below .003 are OK, but cannot prove it. Tough to make all of them cookie cutters.
     
  5. Kevin Thomas

    Kevin Thomas Well-Known Member

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    Hey guys,

    I have a slight problem with threads like this, in that I'm not sure we're all speaking the same language. Everyone seems to have their own methods of measuring run-out, and they're not all the same. Saw this sort of thing constantly in the QC range, with customer complaints of concentricity issues. The vast majority would turn out to be customer errors in how they were measuring what they thought was run-out.

    I'd like to see some sort of standardization on how we measure, so that all our results would corelate to one another in a more meaningful manner. Don't ask me how we do that, but that's what I'd like to see.

    Beyond that, I think we can all agree, less is better. But how much?

    Kevin Thomas
    Lapua USA
     
  6. Mikecr

    Mikecr Well-Known Member

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    There are two standards going(one too many) currently.
    Total Indicated Runout, and Concentricity.

    TIR amounts to any and all combined as deviation from straight or true.
    Concentricity amounts to ~1/2 the same -w/resp to a centerline.

    Concentric ammo might not be staright, but straight ammo is concentric as well.
    So IMO, low TIR should be a reloader's goal.
    The best tool for TIR that I'm aware of is a V-Block/Roller similar to Sinclair's.
    And I assure you, your ammo is not straight until measuring low TIR.

    There are far too many abstracts affecting accuracy to set any rule of thumb. Your chamber clearances -vs- mine, your bullets, throat, headspace, cartridge diameter and length, seating depths, rifling, leade angle, primers, powder.
    I say take it to diminished returns for your system,, and no further.
     
  7. Broz

    Broz Well-Known Member

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    Great Point Kevin.

    I measure at the "O" give of the bullet. And I measure total runout. I don't divide it 1/2 for each direction from center. So total upand down. With Lapua brass that was annealed evenly and using full competition redding bushing dies with no expander. I can get .0005" (1/2 thou.) or less. I usually do 100 at a time and will only have 3 or 4 not make it into this group. They will be .002" or less and are used for practise.

    Jeff
     
  8. Mikecr

    Mikecr Well-Known Member

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    BROZ has straight ammo.

    And he brings up a third standard of sorts; Those who 'halve' TIR to declare pseudo concentricity as 'runout'. And then it get's into neck -vs- ogv also. That's true..

    I declare runout like BROZ, TIR off the ogives.
     
  9. padd54

    padd54 Well-Known Member

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    What tool are you all using to mearure the runout?

    I have the Sinclair tool and am still learning how to get consistant readings off the same case.
    For my 338LM;
    I measure after FL die before neck turning then after, this is when I segragate into three piles; .0005-.001, .0015-.002 and .0025-.003. Anything above .003 I will run through the FL die again to see if I can get it down to <.003.
    I am using Redding Comp dies. Then I measure when the cartridge is complete and segregate again. I have had some of the them actually get better and move down to the next group.
    I have never measured bullet runout, I can't seem to visualize how to hold the bullet in a consistant enough manner to get reliable readings.
    I would appreciate guidance.

    Thanks,
    Ray
     
  10. 300rum

    300rum Well-Known Member

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    Hi Gene,

    Not for the Bullet alone. After seating I checked the Runout.
    As Eaglet sayd, At the beginning after seating bullet to 40 cases batch I got almost half with runout more then 0.003.
    After I paid attention to reloading process I got form 50 round just less then 5 round with 0.003 runout and the rest on 0.001 - 0.002 and also no runout (zero).

    In my setup - when inserting the bullet for seating in case, MAKE SURE IS STRAIGHT AS MUCH IS POSSIBLE. No deviation left right front back, perfect vertical alignment.
    Then lower the seating die till is touching the bullet and when you fill the bullet seats inside just 1-2mm, then retract and rotate the case 180 degree and lower the seating dies to the end.
    Measure the bullet for run-out and you will be surprised.
     
  11. J E Custom

    J E Custom Well-Known Member

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    Very good comments so far and more to come "I HOPE".

    Sounds like I am not to far off but Wanted to know if I could Improve some more or
    not.

    The way I have found that works the best for me "SO FAR". is=

    First I true the necks for turning with a carbide mandrel.

    Then I turn the necks to the desired thickness.

    Next I full length size by starting and relaxing to allow the case to shift if it needs to
    and then trim to length,(I found that if I neck turn first the dies don't push the
    necks off center as bad because they are the same thickness all around) .

    Then I weight sort the brass in batches and indicate the brass for neck run out .If it goes
    beyond .001 then I set it aside and go through a resizing process or just load them to fire
    form them (With a good chamber they will be near perfect).

    After the ones that were .001 or less are loaded ( I use the same method of turning the
    round after starting the bullet).

    This is when I check for total indicated run out at the bullet ojive while restraining the bullet
    tip and case head.

    If This is the wrong way to do it please feel free to tell a better way !!!!!

    At present I can get TIR from .0002 to .0005 most of the time and if some are .001 I will
    separate them from the rest and test them separately but can't tell if it makes a difference
    because of my ability as a shooter. I can say that the rounds that were .003+ do not shoot as well and SDs are not as good.

    Thanks to everyone that has posted and keep'em coming.

    J E CUSTOM
     
  12. Moman

    Moman Well-Known Member

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    +1 on this technique. I FL size with custom honed Forster FL Comp dies with an expander. After sizing, I measure runout at the case mouth along with neck wall variance and make sure they match. As long as they match, I figure any runout shown will be due to neck wall variance and the centers should be true. I don't neck turn so this is the best I can do at this stage. I sort brass by neck wall variance and only keep .001 or better for long range work. This has helped with much better TIR and long range accuracy.

    As far as the magic number, I am striving for 0 runout but usually end up with .001. Lately I've had some problems with runout that I associate with poor brass and a tweaked press. This has absolutely killed accuracy. Some loads jumped up to .006-.011 and accuracy opened way up in the 1" range. A little embarrasing that this snuck by me, but life is life and corrections are being made.

    As 300RUM mentioned, paying attention to all details is critical.
     
  13. Mikecr

    Mikecr Well-Known Member

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    Why on earth would you 'restrain' what you're trying to measure?
    You're masking variance. This is why your numbers are so low.
    Sounds like you're using a concentricity gage rather than a Runout gage.

    As a note, the Sinclair 'Concentricity' gage is actually a 'Runout' gage.

    Why are you guys FL sizing NEW brass & culling by runout?
    New brass could measure any runout, even if turned, until it has been fire-formed into it's final product.

    #1 Stop FL sizing new brass. It is wasted time.
    #2 To see your brass at it's lowest runout(it's best potential), measure it after fireforming, & before doing anything to it.
    #3 Measure after each sizing stage to see the specific runout contributor
    #4 Measure loaded runout off the ogive at a point near land contact, with the bullet unrestrained. Don't assume anything about the neck, or even think about it at this point.
    Think TIR off the ogives.
     
  14. Moman

    Moman Well-Known Member

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    #1: I think when most guys state, including myself, that we FL new brass is not necessarily doing a complete FL size on it. It's simply to run new brass through a die and straighten up the case mouths. Whether I am using Lapua, Norma, or Nosler, they have all improved by running through a die for this purpose. In most cases, the shoulders aren't being touched until fireformed.

    #2: Not every gun has a completely true chamber and some do contribute to concentricity issues. So if you were to fireform all of your brass before doing any measuring, it could also be misleading.

    With some calibers it is hard to fireform every piece of brass before putting the gauges to it. The 300 RUM is a prime example. There is only so much life in most barrels of this and other calibers.

    I agree with you though on the runout gauge. I know we talked quite a bit before regarding concentricity vs runout, and TIR does seem to be a more accurate way to determine this.

    Mikecr, some of this is a little on the newer side to me, and some of it's not. But, maybe this could help to answer the "why on earth would you do that" question.