Drop chart ?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by HDTony, Feb 14, 2008.

  1. HDTony

    HDTony Member

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    I have a question about drop charts.
    First off my range in AZ is at 2100 ft I blast dogs in northeastern AZ at 8000 ft and I am hunting speed goats back home in WY at 5000 ft My 7mm STW is chrono'd @ 3500 fps here at 2100 it's not mine so I was wondering if fps would change at all the locations I shoot at? I would think not.

    Question is do I sight in at my home range and just change my drop charts for the altitude I am shooting at or sight in every time


    Thanks
    Tony
     
  2. britz

    britz Well-Known Member

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    I had often wondered that question too for when I go away on a hunt. I just used JBM calculations and set the zero range at 1 yard and the elevation of 2100 feet. At 200 yards the impact was at 290.2 inches high. When I changed the elevation to 8000 feet, the impact at 200 was 290.3" high (.1" difference). I used 200 yards because that is what I generally sight in my rifle for and adjust from there.

    Please correct me if I'm wrong, but acording to that, you should be able to make a new drop chart using your same Zero but different elevations (you could compensate slightly by imputing the .1" differnce in the sighted in range however).
     

  3. HDTony

    HDTony Member

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    Britz

    cause your the only one that reply to my posts and we are min bro's (born in Calidonia family In Waconia, Branerd (SP), Hallock, Thief River.) Grew up in Casper Wyoming. Now in Queek Creek and Nutrioso AZ. How ya doing in the COLD it 75 here in AZ today
     
  4. HDTony

    HDTony Member

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    I have also set up using JBM calculations. At my Alt it is dead on.
     
  5. britz

    britz Well-Known Member

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    Well, I tell ya. I just loaded up a few batches of 22-250 rds for testing this morning but since it is 3 degrees and 15 mph wind I will likely not get off the couch much today - other than to blow snow. I am a little bumbed since I was hoping to do a bunch of shooting this weekend but it's supposed to be really windy -- oh well.

    I have had pretty good luck w/ jbm too after I figured out that my scope adjusted inches per hundred - not MOA.

    Take'er easy, Mark
     
  6. Jon A

    Jon A Well-Known Member

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    Correct. This is one reason 100 yd zeros are so popular--it'll be even less. If zeroed for 300, 400, etc, your zero will change significantly with altitude so you can't calculate a new dropchart with the same zero.
     
  7. CAM

    CAM Well-Known Member

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    Hello HDTony