Help with math

Discussion in 'Long Range Hunting & Shooting' started by LongRangeNewb, Feb 9, 2012.

  1. LongRangeNewb

    LongRangeNewb New Member

    Messages:
    4
    Joined:
    Feb 9, 2012
    Ok i'm just starting out and i use a .308 with a 21 inch barrel. I want to be able to make 500 plus yard shots but 500 will do for now. I was wondering how to do the appropriate math for figureing out how to adjust my scope to hit my mark. My scope is 4-16x40mm and has 1/4" MOA at 100 yards. I plan to use federal 168gr. match ammo.
    I was told to calculate the adjustment for the drop was for ex. if my bullet drops 63.3" @ 500 to figure the adjustment to do this.
    63.3/1.047=60.458/5=12.091 MOA is this correct? I need help. I would love for now to be able to make a 500 yard to a 600 yard shot gun). please help and thanks.
     
  2. Scot E

    Scot E Well-Known Member

    Messages:
    1,312
    Joined:
    Mar 1, 2008
    There is a free Ballistic calculator on this site that is fantastic for learning what you are after and much, much more. Get to know it, it will be one of the best things you can do to develop a solid base of external ballistics.

    Long Range Hunting Ballistics Calculator

    If you are just trying to figure out the math of it all then you are on the right track. I personally would just use 1 inch per MOA to start because that is really easy and until you verify that your specific turrets actually track at exactly 1.047 MOA then you are really just guessing anyway. Plus out to 500 yards the difference between 1.047 and 1 is nil in the grand scheme of hunting or shooting.

    HTH,

    Scot E.

    PS. Welcome to LRH!
     

  3. LongRangeNewb

    LongRangeNewb New Member

    Messages:
    4
    Joined:
    Feb 9, 2012
    Thanks :). How do I figure my adjustments for wind, spin drift, and the coriolis effect. I'm positive I'm not gonna need to know the coriolis effect because i'm not gonna shoot that far anytime soon. If theres anything else I need to know to pull a 500 yard shot of please share. I'm eager to learn the correct way so I can shoot properly and safely :)
     
  4. Scot E

    Scot E Well-Known Member

    Messages:
    1,312
    Joined:
    Mar 1, 2008
    Ignore Coriolis and spin drift for the distances you mentioned. The program will give you outputs in MOA then you just dial in the appropriate amount.

    4 clicks equals 1 MOA on your turret.

    Scot E.
     
  5. RMulhern

    RMulhern Well-Known Member

    Messages:
    796
    Joined:
    Jan 2, 2003
    It's pretty simple to divide 63 by 5!!
     
  6. Michael Eichele

    Michael Eichele Well-Known Member

    Messages:
    3,829
    Joined:
    Jan 6, 2003
    .25 MOA per click = .26175

    63.3" / (.26175 * (500/100)) = 48 clicks or 12 MOA.

    In other words you are on the right track. You are definately doing it right by taking into concideration the difference between 1 MOA and 1" at 100 yards. At 500 yards it is of little concern. at 1000 yards its the difference between a hit and a miss. Always factor the 1.047 part into the equation.
     
  7. RMulhern

    RMulhern Well-Known Member

    Messages:
    796
    Joined:
    Jan 2, 2003
    DON'T TAKE IT FOR GRANTED....that whatever scope you're using is giving the amount of movement that the maker states!
     
  8. trebark

    trebark Well-Known Member

    Messages:
    3,475
    Joined:
    Jan 16, 2008
    When using ballistic software, have it calculate your wind adjustment for 1mph of wind (for your rifle that will most likely be .25moa per mph out to 5 or 600 yards). Then all you have to do is determine your wind value e.g. 3mph and you know your wind adjustment is .75moa (3x.25=.75)

    I raise this issue because most ballistic software defaults to a 10mph wind value. That makes the math way more difficult than is necessary.
     
  9. load

    load Well-Known Member

    Messages:
    366
    Joined:
    Jan 18, 2010
    lightbulb

    ranging

    size target in yards x 1000 / size of target in mils = range in yardsy

    size of target in inches/moa reading x100 = rangey

    size of target in inches x 27.778 / mil reading = rangey

    size of target in inches x 25.4 / mil reading = rangem



    rpm = mv x (12/twist rate)x 60 =rpm where mv is mean velocity and rpm is rotation per minute

    Kinetic Energy = 1/2 MV2 where M=Mass and V=Velocity



    minute of angle = 1/60 of a degree

    minute of angle = 1.047" at 100 yards

    mRad = 1/1000 radian

    mRad = 3.47 m.o.a. at 100 yrds

    mRad = 3.6 inches at 100 yrds


    vertical wind effect

    1/15 twist = 1/8 of horizontal

    1/10 twist = 1/4 of horizontal

    1/7 twist = 1/3 of horizontal



    wind speed

    angle of flag / 4 = wind speed


    Drop

    minutes to inches at range = 1.047 x range in hundreds of yards(range/100)

    inches X 1.047 / (range/100)= moa at range


    Angle correction

    Drop in minutes X cosine of shot angle = angle corrected drop


    gun)
     
  10. LongRangeNewb

    LongRangeNewb New Member

    Messages:
    4
    Joined:
    Feb 9, 2012
    Thanks for the help :). Is there anything else i should know before sendin a few rounds down range?
     
  11. RMulhern

    RMulhern Well-Known Member

    Messages:
    796
    Joined:
    Jan 2, 2003
    Yep!

    WIND IS YOUR FRIEND!!lightbulb
     
  12. trebark

    trebark Well-Known Member

    Messages:
    3,475
    Joined:
    Jan 16, 2008
    Close your eyes and mash the trigger!:D

    Actually, relax, breathe, exhale, pause, squeeze, bang!
     
  13. load

    load Well-Known Member

    Messages:
    366
    Joined:
    Jan 18, 2010
    spin drift always requires left correction unless you have one of those wierd barrels then of course it doesn'tgun)