drop chart and chronograph drop chart

Discussion in 'Long Range Hunting & Shooting' started by sdriverbottom, Oct 21, 2011.

  1. sdriverbottom

    sdriverbottom Well-Known Member

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    Hey fellas, I recently got a pro chrono digital and the speeds that my chrono reads are roughly 100 fps difference than my actual drop data chart..is this pretty typical (i know there alot of factors that play a part, I was just a little suprised in the difference)
     
  2. highridge1

    highridge1 Well-Known Member

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    miss read your question
     
    Last edited: Oct 24, 2011

  3. WildRose

    WildRose Well-Known Member

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    Yep and keep in mind that the chrono only gives you the actual speed at that point in flight.

    Listed BC's and actual BC's are two different things as well which is why you can build your drop chart according to the MV, and still not be correct at longer ranges. BC changes as velocity changes.

    Start with the MV as verified by the chrono, then verify drops at 3 different ranges such as 200, 400, 600, or 300, 600, 900 and adjust the BC to fit the actual data and then you can have a precision drop chart that will have you plus/minus just a few inches at any range.
     
  4. sdriverbottom

    sdriverbottom Well-Known Member

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    Ok, so if i'm understanding this right..i have my true drop chart..and i'll do a trajectory validation say 500 yards 7moa..and i'll switch my BC until it shows the velocity that my chrono was reading?? Doing it that way I got a BC of .890 ???
     
  5. WildRose

    WildRose Well-Known Member

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    No you adjust your BC until it's reflective of your true drops.

    You start with the MV from your chrony in your initial calculations.

    Take your advertised BC, your MV, plot your drops.

    Then, look at the difference in your drops and what the program spits out and adjust the BC until you have it reading true.
     
  6. sdriverbottom

    sdriverbottom Well-Known Member

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    Alright I believe I have it down now..I started with my chrono MV (3023) and then adjust my BC to match that drop chart with my field proven true drop chart
     
    Last edited: Oct 22, 2011
  7. WildRose

    WildRose Well-Known Member

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    Great. Now take it out and shoot it at some random distances where you didn't do your test shots and you should find it to be very, very close.
     
  8. sdriverbottom

    sdriverbottom Well-Known Member

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    I get a BC of .890 then for my chart..does that seem typical? 300 rum - berger 210 vld
     
  9. WildRose

    WildRose Well-Known Member

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    I don't think so. My guess would be your sight height, zero or one of your other inputs is way off.

    I'm not an expert here but that simply seems impossible with a bullet that size.

    Check all of your inputs.
     
  10. sdriverbottom

    sdriverbottom Well-Known Member

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    I'm having a hard time figuring what my problem is..zero is good at 100, i've checked that many times..sight height is 1.85..chrono was reading 3023 with hsm 210 gr vld..also a few drops are 450 yds - 5.8moa (clicked to to 6 moa shot was good) 500 yds - 7moa, 700 yds - 12 moa...all theses shot hit a 6 inch gong..I would just like things to match up a little better..Thanks guys!
     
  11. WildRose

    WildRose Well-Known Member

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    I was thinking about this while I was out working and doing a little predator control.... .

    I'm wondering if your chrony isn't off... .

    Give me the caliber and load you are using let me play with it...

    I'm thinking possibly you are off a hundred fps or so on your MV.
     
  12. bigngreen

    bigngreen Well-Known Member

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    What program are you using? Verified scope adjustments?
     
  13. mike33

    mike33 Well-Known Member

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    I went thru that crap also with my edge. Chrono says 2750 but i tweeked mv to 2860 and chart works good out to 1220. i believe the chart and would like to trash the chrono.
    mike
     
  14. loosesniper2000

    loosesniper2000 Well-Known Member

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    +1 for Mike33
    If you have 5 different Chronographs you're going to have 5 different readings even if you shoot through all 5 with the same bullet.
    I went through the time and wasted money to figure this out. What matters is where the bullet actually hits. I wouldn't even mess around with the MV and just do like someone suggested and shoot at different ranges, mark your MOA's and go to work on your pc.
    I'd suggest keeping with the b.c and adjust the MV to accommodate your hits, after all it's not about speed. I've found this to be a fail proof system even if the MV may sound a little off. Most guys like to publish the velocity for bragging purposes but that doesn't bother me one bit.
    I just happen to use the Berger 210 in my RUM and when I tested the points of impact at various ranges, my Exbal software showed my velocity at 3090 fps, my Chrony was 85 fps off. Which do you think I'll follow?