shawns video is confusing me but i would recommend

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by tjonh2001, May 12, 2008.

  1. tjonh2001

    tjonh2001 Well-Known Member

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    ok i just got shawns new video its great..... very highly recommended......

    i am wondering what info you input into you pda. during the video he says that you need temp, altitude, humidity and barametric. i knew that. but
    when i am in the field and inputting the information into my pda with exbal i should input all of these things into it to get the best information. during the show though shawn said to calibrate your weather station to 0ft altitude to get the baramtric pressure where you are. if i calibrate to 0ft it will show my pressure where i am but then my altitude will be wrong.

    is he saying to have another devise to get altitude or estimate it? is it more important to use the other info in my weather station. should i jsut leave my pda's altitude at zero?

    or maybe im completly wrong let me know your thoughts.....
     
  2. jmden

    jmden Well-Known Member

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    You don't need to input altitude at all if you're using station pressure. Unclick 'Calculate Standard Pressure', put 0 in altitude and put your station pressure from your barometric pressure device in the pressure box. Make sure your 'weather station' is set to station pressure--the pressure where you are at that time.

    Did I get that right, guys?

    Edit: The barometric pressure at your location is what matters, not altitude. The barometric pressure at you location takes into account altitude and any weather systems that might cause change in the pressure, so there is no need to include an altitude. Knowing your altitude is great, but it has no direct bearing on how the bullet will fly, barometric pressure does.
     
    Last edited: May 12, 2008

  3. tjonh2001

    tjonh2001 Well-Known Member

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    thats what i got from the video. to get my pressure i have to set my skymaster to 0ft altitude and i will show station preaswure where i am right?
     
  4. Shawn Carlock

    Shawn Carlock Sponsor

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    Correct. I enter the elevation anyway from habit but it is not necessary.
     
  5. Eaglet

    Eaglet Well-Known Member

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    tjonh2001,

    On the Barometric Pressure screen of your weather station, when you calibrate it you set the elevation or Altitude = 0; but on the Altitude or Elevation screen, you enter the actual known elevation that you’re at. That way the weather station will give you local on the spot barometric pressure readings and when you change to the Altitude screen you will see the elevation for the spot. I hope it’s clear. You don’t need another device.

    It’s true that barometric pressure is what we care about and not elevation; here is the “but”, according to Exbal’s creator you need to enter the elevation.

    If you zero your rifle at 2000 ft of altitude, you enter all the info in Exbal including altitude and then on the main screen of Exbal you click on “Programs Options”, that gives you a long list if you’re running the latest version which is the one I have, from the list click on “Save Sight-in Conditions” another screen pops up; if the sight in conditions are entered properly, then un-check both boxes at top and bottom and click update. Those conditions will be saved internally and will be used to calculate your new trajectories when you go hunting at 9000 ft of altitude, which you will have to enter in for the program to know you’re now hunting at 9000 feet, enter all the other information as you did when you zeroed in. Do not mess with the previously saved sight-in conditions. This is a powerful reason to enter the Elevation or Altitude. Please do!!!

    I hope this helps.

    Eaglet.
     
  6. geargrinder

    geargrinder Well-Known Member

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    Eaglet,

    Why are you giving advice? You don't even like Exbal!:)
     
  7. jmden

    jmden Well-Known Member

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    Eaglet,

    I'm confused. Try doing what you are saying either in 'field conditions' or in 'save sight in information' and when you enter the new altitude and hit update, you will see the program check the 'calculate standard pressure' and see the pressure value changed to a predicted pressure just as the screen changes.

    The program then makes a predicted trajectory based on the predicted standard pressure for that altitude, which could be somewhat off depending on if there is a hi or lo pressure system in the area. You need to measure station pressure at your new location. That's what's important, not altitude.

    You can put whatever altitude you want in 'field conditions' and the predicted trajectory will not change if 'calculate standard pressure' stays unchecked because the pressure remains constant this way unless you manually change it. However, everytime you go to change altitude, you have to watch very closely as the program will check 'calculate standard pressure' and enter in that calculated pressure (just a number from a table, perhaps quite a bit differnent than actual station pressure) just as you hit update.

    Are we communicating, or am I just muddying the waters? :)
     
  8. Eaglet

    Eaglet Well-Known Member

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    Geargrinder,
    I said I wasn't using it anymore, I've been learning and running the more powerful one LoadBase. I did never say I did not like it. I do like it and very much. If Loabase ever gets too expensive for me , then Exbal is the one. Runs very fast even in slower processors and simple enough to do the job after it has been tweaked to match bullet impacts at different ranges which you have to do with just about any program. I just believe from experience that LoadBase gets me closer and has so many features that I want like correcting muzzle velocities in the field when shooting through a chronograph without having to take my lap top.
     
  9. jmden

    jmden Well-Known Member

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    tjon,

    These weather stations/ watches/whatever make altitude predictions (and that's all they are) based on the barometric pressure. If you really want to know your altitude, use a GPS with good reception to many satellites located in very different parts of the sky, set it down and give it time to really lock in this nubmer--this is probalbly the most accurate and even that will change a bit on the unit. And even if you can pinpoint your location on a topo, you still have to try to estimate your altitude between lines on the map.

    So, as barometric pressure changes with you moving up or down in elevation or a hi or lo pressure weather system moves in when you haven't changed elevation at all, your weather station will tell you that your elevation has changed--a very poor way to get accurate elevation. If you can pinpoint your elevation with GPS or topo and enter this in your weather station, your altitude reading will still change even if you don't change elevation as lo and hi pressure weather systems move in and out of the region. So, altitude by itself in regards to trajectory calculation, in my understanding, means next to nothing. It is station barometric pressure that is the important factor, not altitude, to determine bullet path.

    Now there may be some ethereal calculations that can show that the bullet will change it's flight due to changes in gravitational pull or the coriolis effect or the like if you change elevation drastically, I don't know. But I think that for meat and potatoes LRH, these issue are probably not important. I'm sure there are others on LRH.com that are much more versed in all of this that can set us straight, if that is not the case.

    Good luck.
     
  10. Eaglet

    Eaglet Well-Known Member

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    jmden,
    You are right in that if you enter the BP and enter zero for elevation or enter the on-site elevation it will make no difference. I was explaining why it was important to enter the elevation and I’ll try to explain my self better:

    If in "Save sight-in Conditions" you have the top box checked on,

    [​IMG]
    What ever info. you entered in the "Field Conditions" screen will appear here again, telling the program that whatever is in the field conditons you want to use as your "Sight-in Conditions. At this point when you enter your "Field conditions" info will be also used as your "Sight-in conditions" and as long as the on-site BP is used, it does not matter what elevation you enter in, 0, 500 etc, the results will be the same making you right in what you're saying. So, If you leave the boxed checked as in the photo above you can use exbal that way, Altitude=0 and just change your BP as it changes; and that's the end of it.

    If you want to use Exbal's ability to Use your "Sight-in Conditions" at let's say 2000 ft of altitude, and then without rezeroing at your hunting conditions let's say 9000 ft altitude then you have to take a different approach.

    So that this time I explain my self let's do it from the beginning:

    First we have our main screen,
    [​IMG]
    then we click in order 1, 2, and 3.

    1 is Bullet Data. Click on it and...
    [​IMG]

    2 is Field Conditions. Click on it and...
    [​IMG]
    Enter all info as shown in photo including altitude for the BP.

    3 is Target Engagement. Click on it and...
    [​IMG]
    Enter all the info. as needed

    Now that all of the info for the Sight in spot has been entered,
    you want to save it so that Exbal knows at what conditions including
    altitude you sighted your weapon. WILL CONTINUE...
     
    Last edited: Oct 11, 2008
  11. Eaglet

    Eaglet Well-Known Member

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    CONTINUING...

    Let's click on "Program Options"...
    [​IMG]

    Now let's click on "Save Sight-in Conditions"...
    [​IMG]
    As you remember, the box on top was checked on (for using field conditions) this told the program to copy those conditions exactly to be saved. Now you uncheck the box as in the picture to make sure that for as long as you don't have to re-sight in you want the program to use that info. You don't mess with this anymore. Leave it alone. Now you're ready to go hunting. and when you do you change whatever you have to in steps 1, 2, and 3. Always enter the Altitude for whatever BP and your calculations will be right. If at this point you enter elevation or altitude = 0 you just messed up. You have to keep entering the altitude because Exbal will be doing calculations based on your sight-in conditions and your present conditions. With LoadBase from Patagonia Ballistic you have to do the same thing. You just go about it differently.

    The Altitude box is not there because the programmer is an idiot, trust me on this, he knows what he's doing.


    If you insist on entering zero for Altitude, just remember to do as explained at the beginning of all my bla bla bla. Just don't forget that when you go hunting at 9000 ft of Altitude you have to sight-in again and not at 100 yards because in spite of the Elevation change at 100 yards there is not enough change to be noticed, but you will have a great miss at 1000 yards. Just guessing!

    In any event, that's my understanding of how the program works and if I'm wrong... :eek:
     
  12. jmden

    jmden Well-Known Member

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    Eaglet,

    OK, now I see what you are saying. Thanks.

    Are you still using that itty, bitty boolit? I thought we'd convinced you to go to the 'grande' 240 on top of 103+ grains of US869! :) I'm right at 3K out of a 26" 10 twist with 104.5 gr and 4-6 loadings before primers are loose--some cases worse than others. Quite a wallop without a brake and 10lb rifle, but quite used to it now.

    It appears you're using a bc of .748 for the 'itty bitty' bullet. That's working for you, huh? I think Exbal says .631 for that bullet and .711 for the 240. So far I've found the Exbal predictions to be spot on using it's own bc numbers for the 240, but it would appear that that is not he case for the 210?
     
  13. Eaglet

    Eaglet Well-Known Member

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    jmden,

    I think you did convince me :), the thing is I had alredy too many of the itty bitty bullets...LOL I like that! Also, them 240's are expensive...

    When I use 0.631, at 700 yards I'm hitting high so by tweaking the program come to find out that by using 0.748 :confused: it matches real life out to 1130 yrds... (longest tested).

    With your load, what kind of muzzle velocity you get? That has to be a thumping on your shoulder. :)
     
  14. jmden

    jmden Well-Known Member

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    3K muzzle velocity with loaded rounds at mid 30's to mid 40's temps. I would not shoot this load at over about 55-60 deg. It's not going to blow up or anything, it's just going to lower the life of the brass quickly.

    I ran some numbers in Exbal regarind our above posts and for my load at 1000 yds with about a 7000 ft elevation difference (2950 to 10000) it showed 1/4 MOA difference. So, according to Exbal, you should enter your altitude along with station pressure. Although, as from above, it seems to take a significant elevation change for it to be different by even 1/4 MOA. 1/4 MOA at 1000 yards, however, is one more approx. 2.5 inches I'd rather be accounting for than not! Thanks! It seems like I have to 'relearn' that program every few months.

    tjon, make sure and take this into account. I'm sorry if I misled you.
     
    Last edited: May 16, 2008