Exbal question- What velocity figure do you use ? Fact or fiction ?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Down Under Hunter, Mar 19, 2008.

  1. Down Under Hunter

    Down Under Hunter Well-Known Member

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    Howdy all !

    Just a question for all you exbal users ...

    Does your system use the factual velocity figure tested with the rifle ? It seems that people I speak to have to tweak this number to get the pda to equal actual results.

    I have to inflate my figure to get my ups dead on. Should I stop looking for excuses and just go shoot it and be happy.

    Just looking to see if this problem is unique to me or common place in the real world with exbal.

    Thanks boys

    DUH
     
  2. ss7mm

    ss7mm Writers Guild

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    DUH:

    You got to ask some questions and now I have some for you.:)

    Before you fire the first shot in developing field data and drop charts the only givens you have are the accurately measured field weather data that you have measured and put in your software.

    The next given is the muzzle velocity, accurately measured, hopefully, with your chronograph. After that all else is developed from actual shooting and developing of field data and drop charts.

    Question 1: Do you know what happens to BC when velocity changes?

    Question 2: Do you think that constantly changing velocity, and therefore BC, would cause you to possibly chase your tail in field shooting?

    I believe you'll find that most will accurately chronograph velocity at a given distance from the muzzle, then using that data and all pertinent field weather and environmental data continue and by shooting develop drop charts.

    I believe you'll also find that most will juggle the BC number in their software to get their software calculated data to match up with real world data proven by shooting. Even if you start with a manufacturer stated BC you never know what it actually is in your gun under the current field conditions until you shoot it and develop true data.

    I guess to answer your question I'd say that the data for muzzle velocity that I put in my software is the actual velocity from my chronograph testing and if I tweak any number it would be the BC to make everything match up so the software can then give me reliable first shot data.;);)

    Even when all matches up at say, out to 800-1000 yards, I'd also suggest that you check actual drops by shooting out to the absolute maximum ranges that you'll ever shoot. You may find that you might have to make some slight adjustments at extended ranges.;)
     

  3. royinidaho

    royinidaho Writers Guild

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    Dick,

    Well said!

    Some folks have never chrono'd a load and can put copper on paper @ 1500 plus right off the bat. I was impressed. Very impressed.
     
  4. Down Under Hunter

    Down Under Hunter Well-Known Member

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    Thanks boys,

    I thought I'd ask the question because mechanically my set up is sound. I just cant work out why I have to run a velocity figure of 3096 fps in my edge to get it all my actual drops to match the programme. Apparently the exbal BC is quite accurate. But I know that there are many conditions that can influence results on any given day.

    I have not chronoed the rifle yet, which I have to do.

    To me it all about confidence on knowing that first cold bore shot is going to land where you want.

    Thankyou for answering the question so well.

    Cheers

    DUH
     
  5. Broz

    Broz Well-Known Member

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    I have been doing some Trajectory validation for 1000 because if I use actual MV exbal is about 3/4 to 1 moa high. But then I am low at 600. This is a .338 Lapua @ 2750 1/10 twist. I am using the the .768 BC for the 300 SMK. Should I raise my BC and try it?

    Wa chu think??

    Jeff
     
  6. Ridge Runner

    Ridge Runner Well-Known Member

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    I always use my actual velocity, my actual bar pressure, and altitude at zero,
    I sight in at 300 yards, then shoot at 400, 500, 600 and measure my actual drops, then tweak BC up or down till my actual drops match my chart.
    of all the bullets I've worked with I've found 1 that was "right on" using the published BC
    RR
     
  7. Broz

    Broz Well-Known Member

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    You ment to say haven't found correct?

    I think I will try this. Since exbal is right on at 4,5,6,7, and high at 1000. I would think maybe I need to use a higher BC. The question is, will that screw it up out to 700. I would think not as much??

    Thanks! Jeff
     
  8. Ernie

    Ernie SPONSOR

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    Another feature Exbal has in its BC arena is the ability to list multiple BC's (different BC's for different velocities) like Sierra does.
    This is nice since we are using the G2 system when in fact it should be G7 (hope I remembered the #'s correctly?).
     
  9. Ridge Runner

    Ridge Runner Well-Known Member

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    nope I meant to say have, from all my testing the 139 gr lapua scenar was right on using the published BC of .615, it was pretty well right on out to 1k, noslers are way off, bergers are close!
    RR