Bullet qualification measurements

Discussion in 'Practical Precision--PRS, NRL, ELR' started by Keith Glasscock, Jan 4, 2015.

  1. Keith Glasscock

    Keith Glasscock True believer - Straight 284 Gold $$ Contributor

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    While doing an experiment, I decided to measure up a 300 count of bullets I will be using.

    The measurements I took were the base to ogive length, and the bullet weight.

    My question is this:

    What level of variation in those two measurements makes a repeatable difference on target at 1000 yards? What experimentation have you done? What basis do you use for your determination?

    Thanks,
    Keith
     
  2. bsl135

    bsl135 Site $$ Sponsor

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    That's a good question to ask!

    Many people do all kinds of measurements 'just because' without really knowing if and how much it matters.

    Wish I had some direct test data for you on this one, but best I can offer is that my bullets BTO are within a range of 0.003" and I don't think that results in any measurable dispersion.

    I'll put this on the list of projects to study at the lab. We only have 300 yards there, but we can make very accurate measurements of MV, and see if it varies more for bullets having higher BTO variation. We can also measure BC and look at groups for bullets having the same BTO vs. BTO variations of 0.003", 0.006", etc.

    -Bryan
     
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  3. Keith Glasscock

    Keith Glasscock True believer - Straight 284 Gold $$ Contributor

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    Thanks Bryan,

    On the other measurement, bullet weight, I have a theory that it does not matter that much either. Hypothetically, the reduced MV from a slightly larger mass will have a counteracting increase in BC. I'm not saying that large variations are insignificant, but 0.1 to 0.2 grains does not seem to matter in my shooting (f-class).
     
  4. bsl135

    bsl135 Site $$ Sponsor

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    I agree with your reasoning on bullet weight; the % affect on BC is swallowed up by MV and MV uncertainty.

    There is something else to consider RE bullet weight...

    Depending on how the bullets are made, a small increase in mass, if caused by a physically different sized core, may affect the external shape due to how forces are affected by such things.

    In other words, it's possible that weight variations correlate to things like BTO, or meplat diameter.

    But the effect of 0.1 or 0.2 grains of bullet weight itself I don't think is a significant matter.

    -Bryan
     
  5. 6BRinNZ

    6BRinNZ

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    Bryan - is the bearing surface variance an indicator that other dimensions on the bullet will also vary slightly? Tools to accurately measure bullet dimensions are limited so with respect to myself I measure as much as I can to gain an understanding of each bullets dimensions from one to the next. Bearing surface tests are typically related to MV but the result on paper might be a small group if the bearing surface variance changed other dimensions in turn changing BC thus swallowing up the FPS variance for a positive effect. (?)

    I'm also interested with respect to bullet pointing without meplat trimming and the whidden die. I am working on the theory that if bearing surface is same and base to ogive is same then the bullet is most likely dimensionally the same and therefore it is worth taking the effort to point it and I will have the desired effect of a consistent meplat diameter. Bullet OAL measurement might be useful with respect to a valid measurement for pointing but there seems to be that slight angle on the tip of the meplat which can throw things off.

    Question asked as I don't understand the bullet creation process and therefore understand what dimensions might be linked within that process, with bearing surface being the most obvious measurement having some variance within a given lot.

    TIA
     
  6. Scott Harris

    Scott Harris Gold $$ Contributor

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    A couple years ago I did a 1000 yard test by alternately shooting 16 bullets that had a .012 difference in bearing surface (BSL) during a steady wind. My shots alternated from x-ring elevation to 9-ring elevation. So, I think large variations in BSL definitely matter. These were Berger bullets. I think this only matters at long range and anything less than a .003" variance is acceptable. This test was a long time ago, maybe I'll re-run it.
     
  7. ronemus

    ronemus Silver $$ Contributor

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    Mid Tompkins told me several years ago that he and the clan sort bullets into 1 mg and 0.001" lots. Mid doesn't do any work in the loading room that he hasn't proven is necessary given the volume that the family shoots, and that volume gives him a lot of data to base it on.
     
  8. racesnake

    racesnake

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    Me thinks ol' Mid might have been pulling your leg, a wie bit!!
     
  9. normmatzen

    normmatzen Silver $$ Contributor

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    Scott,
    Your information is very interesting.
    I have a number of times in the past, separated bullets by simple length and by weight. I found literally no difference in performance when grading by weight, and little difference with length. I believe this is because a well tuned load or barrel will allow these small differences in weight and length.
    But, I have thought that bearing length may be the real differentiater.

    I would love to read Bryan's ideas on that.
     
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  10. Canadian bushman

    Canadian bushman Silver $$ Contributor

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    I did a test a while ago with the 215's and varying weight +-.1 gn across 20 cases. I.E. 10 shots with 215.1gn and 10 shots with 214.9 at i think 800 yds and found no discernible difference.

    I think like anything with multiple components the largest deviation is usually a result of "stacked" tolerances.

    This is the largest benefit of sorting, to eliminate the possibility of stacking a light short surfaced bullet on heavy case with a unified powder charge.
     
  11. dannyjbiggs

    dannyjbiggs

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    That saying is correct, but there is more to it! ;) He is also famous for saying, "You weight sort bullets to find the bad bullet(s)...after you've gotten them sorted out, there's no need to mix them back up." 8)

    Danny Biggs
     
  12. g3

    g3

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    Found this thread way too late and probably no one will see this but thought I`d put it up anyway I shoot all wildcats 22 , 24 , 25 and 30. I use Bib bullets as they are wonderfully consistent. A chance came along to get 4 boxes of a major bullet maker "MATCH GRADE" bullets. A quick loading session and off to the range..Might as well been throwing rocks..!!! Measured bullet length--range of .021. Weight was consistent
    Packed these up and sent them back to maker. Waited a bit and gave them a call. I was told that a length spread of that much was within spec. He told me that they took some of what I returned and shot 1" at two hundred yd. He didn`t actually say it BUT between the lines he told me to sort by length. I did so , loaded by case head to ogive length to my usual and retested.. Now in the 2`s at 100yd.

    Since I shoot only single shot LOA is not that big a deal. A thing I might mention here is pressure changes. If you do load by COAL with different length bullets things do change. In a small case like my 25G3 (43.2 gr water) that .020 variance can cause a change in chamber pressure of almost 1000LB and a velocity spread of almost 100FPS
     
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  13. broncman

    broncman

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    My recent sorting of some 185 Juggernauts revealed two distinct BTO variances between 2 lots. Quite a bit actually. Weights were all real close for the 2 lots but BTO was not. I then measured with a Bob Green style comparator( measures seating stem to hornady type ogive comparator) and found both lots to be almost identical. So the ogive profile seemed to match. I then measured OAL and the lot with the longer BTO was also longer OAL.

    So the difference is either in the bearing surface or the boat tail length.

    I did keep the lots separated where as before, I just put them all together...
     
  14. Marksman63

    Marksman63

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    Fellows, a practical way for measuring BTO or would you suggest me a link for that? Thanks
     
  15. Bob Sebold

    Bob Sebold Gold $$ Contributor

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    About 5 years ago I ran a test with weight. I had sorted 1000 Berger bullets into .1 grain increments. When I was done I had about 35 culls. These where all outside .5 grns. Both high and low. These are what you do not want to shoot. I alternated shooting the heavy and light ones on the most beautiful no wind morning in Lodi I have ever seen. I shot a ten shot group of heavy bullets about 1.5 inches centered in X ring, I shot a ten shot 1.5 inch group centered at 10-9 ring junction with light bullets. Light bullets went low which surprised me! I doubt a person can hold even with an F Open rig well enough to tell the difference between 2 tenths of a grain. At least I can't.

    I also can't shoot any tighter than that at 1000 yrds. The problem with this test is getting the most perfect morning, you have to be close to a range and have a buddy who can pull at a moments notice to get this done. Atmospheric conditions can throw your results wildly for elevation, which is what you are testing. Bryan is excepted, I think most people who test at long range fail the testing as a result of this.
     
  16. Dimwit Flathead

    Dimwit Flathead It's the Juggernaut, Bitch!

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  17. Joe Salt

    Joe Salt Silver $$ Contributor

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    I shot a ten shot group of heavy bullets about 1.5 inches centered in X ring, I shot a ten shot 1.5 inch group centered at 10-9 ring junction with light bullets. Light bullets went low which surprised me! I doubt a person can hold even with an F Open rig well enough to tell the difference between 2 tenths of a grain. At least I can't

    Bob if you are shooting ten shots in an inch and a half at 1000 yards, you should be coming to the World Open in PA. in July. It's a $1000 prize money for breaking the record in L.G. and H.G.

    Joe Salt
     
  18. Raythemanroe

    Raythemanroe Bullet Whisperer Silver $$ Contributor

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    Inch and a half 10 shot 1000 yard groups.. Got anyone I have shot with beat..WOW

    My experience (not half as much as some) shows sorting bullets base to ogive, bearing surface, overall length gives much more consistent seating.. Seating in my experience is very important at a 1000 yards..

    Ray
     
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