Ballistic coeficient

Discussion in 'Hunter (HFT) & Field Target (FT)' started by PaulD, Sep 10, 2013.

  1. PaulD

    PaulD I like Feinwerkbau's

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    Location:
    Warrington N/W England
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    Tawd Vale FT&ARC
    Im in a bit of a pickle with my elevation settings :confused:
    after a disastrous first day in Germany where I struggled with my short range settings I did a quick re-zero and guesstimated my dialings from 8 to 30yds. This worked reasonably well but I did have a few unexplained misses at short range.
    On Sunday at the club I re did my settings again by shooting at paper and although I was initially happy when I got home I noticed some of the settings I had written down where a little "odd" compared to what ive had in the past. As im away from home all week the next time I pick the rifle up will be at Weston Park :eek:o
    As a back up im going to do an alternative set up with chairgun just in case my practice on Saturday morning doesn't go as planned! Now ive not had the best results in the past with chairgun but I was told that it works providing you don't use the BC that chairgun gives you. So after that long winded explanation of my woes what do you guys who use chairgun to good effect use as a BC for JSB exacts?
     
  2. burjaka

    burjaka Member

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    CT Sousel - Portugal
    Try ti get some time Saturday to do the cliks.
    Far more effective.
    From 10 to 20 is quite fast to do.
    Good luck.
     
  3. Steve

    Steve Member

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    0.0250 I've always found to be pretty close to real world Paul.
     
  4. Ste Hughes

    Ste Hughes Daystate's whipping boy

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    Location:
    southport
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    I worked it out on my ripley and it was 0.024
     
  5. PaulD

    PaulD I like Feinwerkbau's

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    Thanks guys, at least ill have a fall back if it goes pear shaped :eek:
     
  6. RobF

    RobF Administrator Staff Member

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    Never got chairgun close enough. Main problem is measuring scope height which is done at the muzzle not the breech. Brian Samson has a good idea to solve that but suffice to say if you are seeing shifts there is no substitution for shooting paper.
     
  7. raygun

    raygun Non member

    Chairgun scope height.

    Mark a cross on something like a Yellow pages.
    Set your scope to minimum PA adjustment.
    Cover the Objective lens with tinfoil and poke a small hole (3mm) in the centre of the foil.
    Sight the cross on the yellow pages and with your muzzle as close as possible to the yellow pages fire a pellet.
    You can now measure from the centre of your pellet hole to the cross you've marked.
    This will give you your scope height for Chairgun.

    Originally posted by Harry's Lad, the author of Chairgun.

    Hope this helps.

    ATB
    Ray.
     
  8. SDplinker

    SDplinker Pellet testing...yawn

    Joined:
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    Location:
    Atascadero, CA, USA
    Club:
    CASA - California Airgun Shooters Association
    I'd be interested to see how this program works for you

    RealWorldClicks - written by Chairgun author.

    Give it at least 3 click inputs at 3 yardages and it interpolates the rest. Relies solely on your real world click data (hence the name). :)

    Link in my DropBox: https://www.dropbox.com/s/8jo9wutcgp1yfwy/RealWorldClicks.exe
     
    Last edited: Sep 11, 2013
  9. Brian.Samson

    Brian.Samson Allowed in Sales Staff Member

    Joined:
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    Doncaster
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    Pontefract, Doncaster Airgun Range
    Yup, that's the correct way - Dave (Harry's lad) was actually quoting Steve_in_NC from the yellow forum, not sure where Steve's info came from, but I know that the calculations for Chairgun came from Steve (and they're actually available as open source).

    I've had discussions with people in the past who insist that they're using mega calibrated verniers yada yada to measure the exact physical scope height, but this will almost always be wrong. No matter how accurate your ruler is, it will be wrong.

    I even drew a little diagram to illustrate why it's going to be wrong. > Here <

    The other factor that people can get wrong, especially with regards to clicks, is they assume that a turret marked up as 1/8" clicks, are actually accurate. They aren't accurate quite a lot of the time. There is a method you can use to find out what the real figure is, but like all of these measurements it can end up being more of a hassle to get the correct inputs for ballistic programs than it would be to just pin up bits of paper at all the distances you're interested in and shoot groups.

    That would always be my recommendation - shoot groups on bits of paper if you want the correct answers. Ballistic calculators are useful for 'what if' scenarios, but I wouldn't trust them to give me the clicks for my turret before a competition.

    I did a little bit of testing a few weeks ago with my TX200 and found that the measured BC figure for the batch of AA Fields I've got is between 0.020 and 0.025 at 55 yards. The measured BC for a batch of Daystate selects I have was 0.025 to 0.027. But using 0.024 will get you very close (if all the other measurements are correct, or close to being correct)
     

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