Dope help

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by cowboyarcher, Oct 16, 2013.

  1. cowboyarcher

    cowboyarcher Well-Known Member

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    Hi guys,

    I'm just getting started into the long range game and am having some trouble doping my shots.

    I'm running a 77gr Nosler at 2915fps, zeroed at 100 yards from an AR15. I'm using the listed BC of .340, am at 7200' elevation and am using both the Nikon and isterlok apps to calculate come up values. At 700 yards the apps had me dial 18moa and at 425 yards they called for 8.25moa. I was high at both ranges and was landing rounds on target at 14moa and 6.5moa respectively.

    My weather input is coming from the Weather Channel app data.

    What bad inputs am I providing my ballistics calculators to get false outputs?

    Thanks guys and God bless,

    Adam
     
    Last edited: Oct 16, 2013
  2. MudRunner2005

    MudRunner2005 Well-Known Member

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    What caliber rifle?
     

  3. cowboyarcher

    cowboyarcher Well-Known Member

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    It's a 22 PDK. So basically a necked down and slightly improved 6.8SPC. It running from a 20" WOA barreled AR15.
     
  4. MudRunner2005

    MudRunner2005 Well-Known Member

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    Sounds pretty cool...Can you post up some pics of the ammo and stuff?
     
  5. SBruce

    SBruce Well-Known Member

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    Hello Adam,

    After much messing around tweaking numbers, the only way I could get my program to match even close to your real world results ( 6.5 MOA @ 425 yds and 14 MOA @ 700 yds) was to input a 1" sight height, 125 yd zero, 70°F and 23.37 InHG, 3030 fps and .4 BC.

    There are tons of possibilities why things could've went wrong.

    Chronograph error. ??

    BC not what is published. ??

    Scope didn't click exactly what is advertised. ??...........Check This!!

    Different shooting position or rest or bag for the shots (example, bench at 425 and bipod at 700). ??

    Different lighting conditions or different days between each distance (shot 425 during morning and 700 evening). ??

    The list goes on and on unfortunately.
     
  6. cowboyarcher

    cowboyarcher Well-Known Member

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    It was 2 different days but the conditions were almost exactly the same. . . I suppose I could have a chrono or BC issue, I was also wondering if my barometeric pressure input was off? How would I check my scopes clicks?

    I just found that Litz lists this bullet at .377, that brings things a little closer...
     
  7. SBruce

    SBruce Well-Known Member

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    Ideally you'd want to shoot 2 or 3 distances all during the same day, same conditions and same rest/shooting position. After a few times of doing this and recording the data (shoot paper if possible) then you'll have a pretty good average of what your true "real world" drops are.

    Best way to check your scope clicks is to shoot a group at exactly 100 yds.
    Then, dial up what should be 20 MOA on your elevation dial.
    Next, shoot another group at the same paper but aiming for the original aiming point..............You should end up with 2 groups approx. 20-21 inches apart vertically.

    Now, measure the distance between the group centers and divide that by the number of clicks you dialed. If your rifle is shooting good tight groups, this will tell you how many "real world" clicks it takes to dial in your drops. Last scope I did this with, indicated my clicks were actually .36 MOA per click. I verified it a couple more times (once with 10 minutes and once with 15 minutes) just to be sure.
     
  8. royinidaho

    royinidaho Writers Guild

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    One consideration would be that the weather channel (I think?) and the local airport report pressure corrected to sea level.

    Make sure the value is the absolute pressure at your elevation.

    Sea level runs around 29 something. I'm at 4488 and it runs around 25 something. Up at 9200 feet the other day it was around 20 or 22 something.

    FWIW
     
  9. cowboyarcher

    cowboyarcher Well-Known Member

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    You're right, the standard pressure at 7200' is 22.49 inHg. The Weather Chanel app was reading 30.08 this afternoon. With the corrected BC and pressure, the app is within .25 moa at the 425 yard target and 2 moa at 700 yards.

    Guess I need to plan a day to build some drop charts in the field to get the best numbers.