Air Density Adjustments For Ballistic Drop Reticles Or Turrets

Discussion in 'Long Range Pursuit TV, Gunwerks, GSeven' started by Len Backus, Mar 27, 2012.

  1. Len Backus

    Len Backus Administrator Staff Member

    Messages:
    6,356
    Joined:
    May 2, 2001
  2. Clubhunter

    Clubhunter Well-Known Member

    Messages:
    87
    Joined:
    Jan 12, 2014

    Just so that I am clear, in the example of the video, you would add or subtract both temp and elevation combined correct. So if there was 2 MOA for elevation change and the temp was 20 degrees colder then I would add another 1 MOA bringing the total to 3 MOA difference than what the scope was sighted in at...please clarify and thanks.
     

  3. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,262
    Joined:
    Aug 10, 2003
    No
    The guy that did this video needs to review this thread:
    http://www.longrangehunting.com/forums/f19/altitude-vs-barometric-pressure-11950/
    He needs to stop making generalizations with altitude, and start measuring/using actual air density parameters: absolute pressure, temperature, relative humidity.
    These directly affect both BC, and MACH (which again affects BC per velocity)(Mach is temp and Rh).

    Drop compensating gimmicks are already compromising to accuracy. You don't need additional errors on top of it.
     
  4. Litehiker

    Litehiker Well-Known Member

    Messages:
    943
    Joined:
    Sep 15, 2012
    Good video. You can do all the steps recommended...

    OR get a Kestrel/AB 5700 ELITE that, with your correct input of ballistics before the hunt and input of distance during the hunt, will calculate all of this for you and give you a very accurate firing solution.

    I use Bushnell's ARC 1 Mile 10 x 42 LRF binoculars for correct distance whether horizontal or angled.

    Eric B.
     
  5. del2les

    del2les Well-Known Member

    Messages:
    53
    Joined:
    Oct 24, 2007
    Agreed! With all the accurate tech today, why worry about making more errors. I take a reading from my Kestrel, the GPS altitude and plug it in into my ballistics program on my phone. In a few seconds I have minimized the potential errors and have the needed drop solution in either MRADs or MOAs. Then when the game is located, I lase and can either use an accurate holdover or dial the turret.

    This is one of the reasons I do not use special yardage turrets on my scopes, for hunting near sea level at 70-80+ degrees with 70% humidity to 9,000 to 14,000 ft and/or sub zero temps changes everything.
     
  6. Litehiker

    Litehiker Well-Known Member

    Messages:
    943
    Joined:
    Sep 15, 2012
    I would never buy a scope with a "BDC" reticle due to their limitations. As one optics expert said in an interview, "...BDCs lie to you beyond 400 yards."

    Instead I use a mil/mil turret and reticle for my SWFA 3- 15 x 42 hunting scope and a mil/mil Bushnell ERS 3.5 - 21 x 50 tactical scope with a Horus H59 "Christmas tree" milling reticle for long range competition on my Ruger Precision Rifle.

    Both of these rifles are in 6.5 Creedmoor using 143 gr. Hornady ELD-X for hunting and 140 gr. ELD-M for competition. The ballistics are nearly identical so I get very familiar with that trajectory curve and wind drift. Both bullets are nearly identical in shape and G1 and G7 BCs.

    Eric B.