CONCENTRICITY GAGE ?? Reloading for 1000 yards and beyond

Discussion in 'Reloading' started by bigbuck, Aug 28, 2012.

  1. bigbuck

    bigbuck Well-Known Member

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    Okay I think I need to take the next step with my reloading . I have vertical shot patterns that would be small and tight if I could get my vertical spread down. So , do I need to buy a concentricity gage ? To measure my bullets and see if they are in line with center of the neck ? If they measure to be off what then? Do I need to buy another tool ? Needing advice from someone who has been down this road before ?
    Thanks in advance.
     
  2. Bart B

    Bart B Well-Known Member

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    Too much muzzle velocity spread's the most common cause of vertical stringing at long range. In second place is the barrel's got bedding under its chamber area; totally free floating it's typically better.

    If you're shooting prone, not putting the butt pad in the same place vertically in your shoulder also causes vertical shot stringing.

    What cartridge are you using and what's the load recipie? Are you metering powder charges direct into the case or do you weigh each charge?

    Concentricity gauges only tell you how straight the bullets are in your reloaded cases. The smaller the number the more accurate the ammo will be. But it's hard to see the difference in virtually all chambers when the runout's .003 inch or less.
     
    Last edited: Aug 28, 2012

  3. Joe King

    Joe King Well-Known Member

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    Whats your load, ES,SD?
     
  4. Trickymissfit

    Trickymissfit Well-Known Member

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    good post Bart!

    I have the same issue with the butt pad, but I'm steadilly working that problem out. You also can get it from the front rest as well, but the amount it gives will vary. High velocity increases bullet spin and thus increases the error in the C/G (.0001" in the C/G is known to give .093" spread at 100 yards). But on the otherhand that spread will also go sideways as well as vertically.

    Another way to cause the groups to spread vertically is with a muzzel brake. Most folks don't reallize this, but it will.
    gary
     
  5. Bart B

    Bart B Well-Known Member

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    Thanks, Gary.

    I believe the muzzle brake on M14NM's when TRW first made them was the brake's hole was too small; rain drops settling at their bottom (damned gravity!) caused vertical shot stringing. The US Army Marksmanship Unit spec'e the hole much bigger, reamed out the ones they had. . .no more stringing The USMC team shop did the same thing. As this was an "internal modification" it was within the DCM and NRA rules for service rifles. A few folks forgot this problem making M1A's into match grade rifles. I wonder how many bolt gunners know about this. Lots, now, probably from reading about it here.
     
  6. lrdevil

    lrdevil Active Member

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    Consistency is the name of the game, anything you have that can indicate how consistent your loads are from one round to the next will be good to help you narrow things down. My opinion is do what you gotta do to eliminate variables, a concentricity gauge can be helpful. Ladder test your loads also at a good range like 600 yards or so. I dont do a complete round robin ladder test but I will start at a good modest load and just shoot from there up to see which load provides the least vertical spread is and thats the load I work with.
     
  7. bigbuck

    bigbuck Well-Known Member

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    I use a rcbs 1500 scale to measure my powder charges. I have a DE brake (shawns) .
    My SD and ES are not in the single digits. I have it written down I'll have to find it tho.
    I am shooting 7 7/8 inch 3 shot group @ 1000 yards. If I could get the vertical spread down I could shrink my groups a little.

    Thanks for the reply's
     
  8. Bart B

    Bart B Well-Known Member

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    What cartridge are you using?

    If the powder used is too slow for consistant pressure curves, that can cause too big of a velocity spread.

    Seven inch range for groups is about as good as long range benchrest rifles shoot. Those tiny 2 inch ones bragged about are at the small end of statistical luck.
     
  9. Hunter2678

    Hunter2678 Well-Known Member

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    AKA "interwebs shot groups"..:D
     
  10. Trickymissfit

    Trickymissfit Well-Known Member

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    was news to me, but makes a lot of sense
    gary
     
  11. bigbuck

    bigbuck Well-Known Member

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    I shoot a Remington model 700 .300 RUM with a broughton heavy barrel 26'' DE brake. wyatt extended box mag, 210 bergers 85 grains of Retumbo federal 215 Match primers .

    I have a thread in the longrange hunting shooting section of the forums . You can see my set up I shoot off of the top of my saburban . prone . I am just getting started .
     
  12. Joe King

    Joe King Well-Known Member

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    Might give H1000 a try, from what I've seen ES, and SD tend to be a little larger with Retumbo.
     
  13. bigbuck

    bigbuck Well-Known Member

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    I have some h-1000 on the loading bench as of now . I didnt get it to group as well at 200 yards as the retumbo but I didnt put as much time into it as i did with the retumbo. Maybe I can try it again .

    Thanks for the help and advice to all who has replied.
     
  14. Bart B

    Bart B Well-Known Member

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    Try a 10-shot group without the magazine installed.

    Detachable box magazines don't all fit the action parts with the same contact and tension. When M14NM semiautos were first used in competition, top competitors found that they had to use two magazines that made bullets shoot with good accuracy as well as to the same point of impact for 10-shot rapid fire strings; one with the first two rounds and the other with the last eight. Otherwise,a 1/2 to 1 MOA error happened between two of them. Then find another tight fitting magazine that held its position relative to the action exactly the same for each shot for slow fire at long range. Any relocation of the magazine to the action between shots from recoil is guaranteed to change the way the barrel whips and vibrates for that particular fit.

    I doubt yours is any different. If it is, that's great.