Am I calculating balistics in Altitude correctly?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Coyboy, Oct 7, 2006.

  1. Coyboy

    Coyboy Well-Known Member

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    I went to JMB calcs and set the numbers for my load at 900ft. This particular load runs 1000ft lbs to 700 yards.

    Same load at 11,000 ft altitude keeps 1000 ft lbs out to 1000 yards. Is this correct?

    I kept the standard atmospheric conditions at JMB's default setting, and checked on the box that states "standard atmosphere at altitude".

    Did I do this correctly?
     
  2. JBM

    JBM Well-Known Member

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    Probably. Without knowing the other values you put in it's hard to tell. The atmospheric density at 11000 feet is only 70% of what it is at sea level so I'd tend to believe it.

    Brad
     

  3. Coyboy

    Coyboy Well-Known Member

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    Thanks JBM.
     
  4. CatShooter

    CatShooter Well-Known Member

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    [ QUOTE ]
    I went to JMB calcs and set the numbers for my load at 900ft. This particular load runs 1000ft lbs to 700 yards.

    Same load at 11,000 ft altitude keeps 1000 ft lbs out to 1000 yards. Is this correct?

    I kept the standard atmospheric conditions at JMB's default setting, and checked on the box that states "standard atmosphere at altitude".

    Did I do this correctly?

    [/ QUOTE ]

    Nope. "Standard atmosphere at altitude"... will give you the "Standard atmosphere conditions", which are 59 degrees, 78% humidity, and 0 feet above sea level.

    Un-check it and try again.
     
  5. Coyboy

    Coyboy Well-Known Member

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    Catshooter, Tried it checked and unchecked, the difference in the calcs is 30 ft lbs and 2" @ 1000 yards. So when checked it is still calculating at the elevation that was entered.