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Thread: statistical comparison of Magnetospeed and Labradar data

  1. #1
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    statistical comparison of Magnetospeed and Labradar data

    Question for the statisticians:

    I am doing load development for a few different cartridges with a couple different bullets and/or powders in same of the cartridges.

    Where I could, I shot the test rounds on both the Magnetospeed and the Labradar.

    What statistical test would one use to compare one data set to the other? Does one device tend to measure higher or lower than the other, or are the differences within the typical variation round to round?

    It was surprising the number of times they registered the same velocity. There were frequent differences of a few/several fps, but I would have to go back and review the readings to see if one chronograph consistently measured higher or lower. I kind of think there is no clear favor to one chrono to the other. Several times there was a difference in the teens.

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    Post the raw data if you have time, that would be neat to see. For this kind of thing, a string having lots of shots in it would be helpful.

    Look at the SD when using the Magnetospeed data vs the Labradar data. If one of the chronographs pretty consistently has a smaller SD, then it is the more precise of the two. This is because random error produced by the chronographs will scatter the velocity readings. If the error is not random, then it would influence the average velocity so compare that too for a trend.

    That being said, being the owner of a Labradar and having never touched a Magnetospeed, I can tell you that the Labradar is better.

  3. #3
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    Interesting comparison, curious to know what the percentage difference between the labradar and magnetospeed are as an average. Thanks

  4. #4
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    bullet Sierra 142 HPBT - #1742
    Powder Reloader 16
    1 2 3 4 5 6 7 8 9 max 0.3 gr step
    41.2 41.5 41.8 42.1 42.4 42.7 43 43.3 43.6 43.9 grains
    2700 2800 fps
    43.5 was Sierra supp max
    magnetospeed
    2721 2721 2738 2762 2796 2826 2839 2837 2872 2860
    2690 2718 2726 2777 2807 2805 2819 2838 2871 2867
    2703 2716 2759 2787 2768 2804 2823 2835 2853 2879
    avg 2704 2718 2741 2775 2790 2811 2827 2836 2865 2868
    ES 31 5 33 25 39 22 20 3 19 19

    Labradar
    2724 2708 2734 2763 2793 2823 2834 2832 2874 2861
    2691 2721 2724 2771 2793 2805 2825 2834 2869 2866
    2703 2712 2759 2789 2767 2807 2822 2833 2853 2871
    avg 2706 2714 2739 2774 2784 2812 2827 2833 2865 2866
    ES 33 13 35 26 26 19 11 2 11 10

  5. #5
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    Interesting. With large enough sample size, get similar average. But different extreme spread. So which chronograph do you trust enough to express accurate expression of consistency?

  6. #6
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    They are only off each other by a few feet so I would say that both are pretty consistent. It mainly comes down to how much do you want to spend and the ease of setup.

  7. #7
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    I had some time last night to graph them against each other. The lines essentially overlap and they cross over each other equally.

    My statistics classes were years ago. It seemed like correlation coefficient or co-variance or something would numerically relate the numbers; along the lines of multiply Labradar by 1.1 to get the expected Magnetospeed or something.

  8. #8
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    I had statistics back in '96 and didn't get much out of it since the instructor's accent was so thick he was hard to understand.

    My magnetospeed does most of my chronoing since I made a free float mount for it to eliminate the barrel attaching. Shooting chrony still handles pistol and short barrel duties.

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