help with drop field ... exball and field resoults

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by 300rum, Feb 7, 2010.

  1. 300rum

    300rum Well-Known Member

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    hi,

    i got a strange situation...
    i have a big difference on drop value from one day to another at diff distances.
    2850fps, 300smk, 49f, 40%humidity, 24.75 pressure. 2mph from 3 clock
    the same batch of reloading bullets, 0.5-0.75moa all day.
    all the shooting are done from one slope to another over a small valley.
    wind is blowing acros the valley, from 3 to 9 a clock.
    so here is...
    exball or jbm value are the same but real field value are off
    407yrd - exbal 5.2moa, but field is 4moa
    620yrd - exbal 10.75 but field is 10.5 at 8 degree cosine
    975yrd - exbal 21.75 but field is 22.75 at 0 cosine

    i double cheked everything, and this is drive me nuts...
    any adviced, or help to solve this will be more then welcome.
     
    Last edited: Feb 8, 2010
  2. bigngreen

    bigngreen Well-Known Member

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    Could you post scope height, zero range and height and what BC your using.
    I couldn't get it to line up with the short and long but the 620 was close.
    Maybe elevation also.
     

  3. 300rum

    300rum Well-Known Member

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    zero - 100yrd
    scope - 2.345

    alt . 5374ft
    press - 838
    i used multipe bc;
    0.795 - 3150
    0.780 - 2600
    0.770 - 2400
    0.630 - 2180
    0.590 - 0

    or g7 - 0.383
     
    Last edited: Feb 8, 2010
  4. bigngreen

    bigngreen Well-Known Member

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    I guess I don't see the answer, I was wondering if you have verified scope adjustments as true. Also, were all shots cold bore or is your measurement off a grouping, are you sure about your range. I could get within a couple 10ths at the 620 and 975 but the 407 was 1MOA+ high. Hopefully someone will have some more ideaslightbulb
     
  5. roaddog1m

    roaddog1m Well-Known Member

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    I was reading rather quickly so I may have missed it but, what was the temp on the day when you chrono'd your load?

    Also, on the day that you were out shooting, had you laid your ammo in the sun or could they have been exposed to heat?


    Tom
     
  6. Eaglet

    Eaglet Well-Known Member

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    300rum,

    I'm using G7 which I beleive is more accurate than using multiple BC's from G1.

    That said, from my figured numbers, if I did it right, you know how that goes, garbage in garbage out; these are my conclusions:

    1) From my number to your field results, the bullet impacted 6.9" low.
    2) Again, following the same thinking, the bullet impacted 2.6" low.
    3) Once more, the bullet impacted 6.64" high.

    As mentioned above, seems like your ammo was in the sun; you can see how the bullet impact is moving gradually higher; or, you were shooting your groups without letting the barrel cool down enough... Once the barrel starts getting hot, if we leave the ammo in the chamber for little longer than a short time, it'll be enough to get higher muzzle velocities and impact higher as it gets warmer.

    Then again, the differences are not that huge and shoulder pressure from group to group could do that.

    If you chronographed the load, what kind of spread are you getting?

    The numbers for vertical adjustment I got were: 5.4 moa; 10.9 moa; and 22.1 moa.

    I hope it helps...
     
    Last edited: Feb 9, 2010
  7. 300rum

    300rum Well-Known Member

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    This happend all the time to this shooting location
    See the photo bellow
    [​IMG]

    I used swarowski range finder - multiple reading and got the same distance
    The shots was at cold bore shot 4 moa at 400yrd, and the other 3 round at the same impact 4moa
    Please note I used H1000 powder so no fluctuation on temperature.
    Temp was 41F to 49F during shooting session., and the ammo was left on plastic case with the lead on, so no sun exposure.
    3 shots, let the barel cool down, and no changes in elevation.
    It sound strange but this can be the wind? the wind from the valley?
    At the target and at the shooting location wind was 2-3 mph from 3 a clock.
    Please note This happend all the time at 400yrd at different day, or different temperature.
    I was in fall 2009, ian 12 2010, feb 4 2010, and all the time shooting at 400 yrd at the same target location (see the photo) over the small valley I get the same 4 moa elev. I know is off from 5.25Moa (JBM, Berger, Exbal) prediction, but I tried to get a logical explanation.
    The fanny thing is if I go at 2200elev, on plain field and shoot at 400yrd, the 5.25 MOA match.
    So by excluding one by one, I suspect the hidden wind from the valley bellow, can cause the almost 1.45 Moa difference.
    Did you experience the same off value from shooting over a valley?
     
  8. Eaglet

    Eaglet Well-Known Member

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    That sure is a great photo of a beautiful place...

    I think you're going to be right!

    If you haven't read this you'll like it.

    Reading The Wind
     
  9. 300rum

    300rum Well-Known Member

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    Hi Eaglet,

    Yes it is a nice country with lots of open spaces.
    I reread Shawn Articles about the wind over canyon and I think this happens with me.
    Now I got why 2 yrs ago I miss a bear in the same spot 624yrs shooting just one hand over the shoulder. The same think shot over the canion (valley) with small wind blowing over from 6 a clock at 5 mph.
    At that distance clear miss.
    Damn ... I have to shot more often to get right wind reading.

    Thank you Eaglet, and all of you... next week I will head back for more shooting.

    Here are some more images of the place 975yrd shooting
    [​IMG]
    and the target less then 10in at 975yrd - realy easy and boring... with my 338edge and 300smk
    [​IMG]
    the fresh spots was fiew of the rocks busted.
    In the image is the new painted rock ready to be busted with 300smk at 975yrd
     
    Last edited: Feb 9, 2010
  10. bigngreen

    bigngreen Well-Known Member

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    I have a spot that is sure fire for deer and elk coming into the edge of the timber from a sagebrush face that is real hard to figure out, from the shooting position there is zero wind but at 720yrds I have seen 6MOA of windage with a little lift, I'm going to shoot it this summer and get it figured out.
    Wonder if the wind is tumbling up the draw not just easing throught?
     
  11. Eaglet

    Eaglet Well-Known Member

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    300rum,

    Not all of us are walking 1000 yards... That's a long walk! :D

    I'm with pics what a child would be with candies.

    That's a cool camera, do you mind stelling us what it is?

    Keep us posted!
     
  12. 300rum

    300rum Well-Known Member

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  13. Eaglet

    Eaglet Well-Known Member

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    Thanks,
    impressive quality for 5 mb, one of my sons had a little Nikon with 3 mb that would always impress me. My pocket camera has 10 mb and does not excite me that much. :)
     
  14. 300rum

    300rum Well-Known Member

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    I know, I get rid off of 10mb digital camera just because of the quality of the images. It was worst, and when you zoom in you can see all the pixels very bad.

    This is just because they emulate now 10mb by software, and at the old digital cameras 5mb is real not emulated.