Ready to sight in and develop range card

Discussion in 'The Basics, Starting Out' started by Alan Griffith, May 16, 2007.

  1. Alan Griffith

    Alan Griffith Well-Known Member

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    Aug 22, 2005
    The load is developed, the new IOR 3-18x42mm is mounted and bore sighted, the rifle is basically set up and ready to go. I should be getting Exbal and Palm by July.

    I want to now develop a 1600 yd range card. I figure to start using http://www.eskimo.com/~jbm/calculations/traj_card/traj_card.html.


    Their are some entries which I'm not sure of. The following is what the entries are.

    -Nosler 30 cal 180 BT
    -BC of .507
    -Muzzle vel 3050 fps
    -Chrono screen distance of 10 ft from muzzle
    -sight height above bore = 1.9"
    -sight offset? What's that?
    -Azimuth? What's that?
    -Elevation?
    -Zero height? What's that?
    -LOS angle? I assume Line Of Sight?
    -Wind speed, I'll put in 1mph
    -Target speed, what is the walking speed of deer/elk
    -Zero range, I'll put in 100 yds
    -Temp. I assume I put in the expected temp on the day I'm shooting
    -Pressure. Where do I get that?
    -Relative humidity. where do I get that info?
    -Altidude. That one I know how to get!
    -Vital zone radius. I assume if 10" is the vital zone of an animal, that is the entry; 10.
    -Drop units. Does it matter if inches or MOA?
    -A few of the next 6 checked boxes I think I understand, like Range in Meters would be meters instead of yards/ and / Zero at Max PBR /The first 4 i'm not so sure of. I can guess but would prefer help on.

    Thanks for any assistance you can offer.

    Big Al
     
  2. royinidaho

    royinidaho Writers Guild

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    I'm on the same trail as you are but a bit behind per Exbal. It's taking me about 2 shots to figure out the environmental conditions at distance.

    Go here for your meteorological stuff. If I knew where in the heck Hobble Canyon is I'd provide a direct link. /ubbthreads/images/graemlins/confused.gif

    Utah Weather Reports
     

  3. Alan Griffith

    Alan Griffith Well-Known Member

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    Roy,

    Thanks for the link. I wonder if the pressue for a certain town is adjusted/corrected. Not sure what I mean, but I know it's not the correct pressure to enter into your Exbal program. I think it needs to be based off something like that from a Kestrel Pocket Weather meter. I believe meter is supposed to be set from something like a local airport which should have the actual pressure.

    I live near the mouth of Hobble Creek Canyon which lies between Springville and Mapleton, Utah.
     
  4. CatShooter

    CatShooter Well-Known Member

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    [ QUOTE ]
    Roy,

    Thanks for the link. I wonder if the pressure for a certain town is adjusted/corrected. Not sure what I mean, but I know it's not the correct pressure to enter into your Exbal program. I think it needs to be based off something like that from a Kestrel Pocket Weather meter. I believe meter is supposed to be set from something like a local airport which should have the actual pressure.

    I live near the mouth of Hobble Creek Canyon which lies between Springville and Mapleton, Utah.

    [/ QUOTE ]

    The pressures are corrected to what they would be at sea level.

    To use them, enter the pressure you get from the site, and the altitude where you are (3,500 feet AMSL)...

    ... or enter the local "true" pressure you get from a Kestral and enter "0" for altitude - either will give you the same shooting solution.

    Never enter the pressure from the weather station, AND your altitude together... you will get double the correction and shoot high at long range.

    .
     
  5. Alan Griffith

    Alan Griffith Well-Known Member

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    Catshooter,

    Very well explained! Thank you very much. I was wondering how they worked jointly or not.

    Big Al
     
  6. CatShooter

    CatShooter Well-Known Member

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    [ QUOTE ]
    Catshooter,

    Very well explained! Thank you very much. I was wondering how they worked jointly or not.

    Big Al

    [/ QUOTE ]

    My pleasure...

    What is not understood by most shooters with these programs is that the software does an "internal" correction.

    All weather stations take their local pressure, then correct it to sea level. So in Denver, they will get a true pressure of 23", and then add 6" to it (1,000 feet = 1" pressure, Denver is at 6,000 feet AMSL).

    So when Denver says the barometric pressure is 29", it means that outside the window, it is 23", and they have corrected it to 29".

    This is done so that weather stations around the country can watch weather fronts move across the country, and they are all speaking the same language (so to speak).

    Also... when a pilot lands at Denver, he sets his altimeter to 6,000, and his barometer to 29" and then his instruments are accurate and match his maps wherever he flies. (At least that was the way they did it in the days before GPS /ubbthreads/images/graemlins/wink.gif /ubbthreads/images/graemlins/wink.gif )

    .
     
  7. lazylabs

    lazylabs Well-Known Member

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    That's not entirely true. If it were you would always have a set pressure for a given altitude. There is a correction for altitude but you must include temperature and other factors to get a corrected density altitude. I am not sure if you are saying the program is figuring that or not. It's true that if you know a fixed altitude you could adjust an altimiter to read that number and use the derived pressure number. True?
     
  8. CatShooter

    CatShooter Well-Known Member

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    [ QUOTE ]
    That's not entirely true.

    [/ QUOTE ]

    Actually... it is entirely true!

    [ QUOTE ]
    If it were you would always have a set pressure for a given altitude.

    [/ QUOTE ]

    I'm afraid that you didn't understand what was said.

    Nothing was said about a set pressure. The discussion was about how local pressure is reported, and how to enter it into shooting computer programs - and why you must either enter the true local pressure and enter "0" as altitude, or enter the local "adjusted" pressure, and then enter your actual altitude... there was nothing said, or implied, about set pressure.

    Let me make it simple. In a state like California, you can be at sea level, and a few hundred miles away, you can be at 12,000 feet.

    If a weather front in aver California, and the pressure at the coast is measured at 30", a few hundred miles away, the measured pressure will be 18". Now, if both stations report their pressures to the state's weather bureau, it will make no sense, because it's the same weather system... so the station at 12,000 will add 12" to their pressure, so it all "normalized" to sea level. in the way, the weather bureau can plot the isobars across the whole state, and map out the weather fronts.

    It is done that way all over the world.

    So your problem is...

    [ QUOTE ]
    There is a correction for altitude but you must include temperature and other factors to get a corrected density altitude.

    [/ QUOTE ]

    Sorry... this discussion was about the relationship between altitudes and software corrections.

    EVERYBODY knows that temperature is part of the final shooting solution, but that is not pare of the discussion here, and temperature does NOT effect the entrance of altitude parameters into the software.


    [ QUOTE ]
    I am not sure if you are saying the program is figuring that or not. It's true that if you know a fixed altitude you could adjust an altimiter to read that number and use the derived pressure number. True?

    [/ QUOTE ]

    I don't understand why this is a confusing issue.

    .