Help with math

[LongRangeNewb]

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.

 

[Scot E]

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!

 

[LongRangeNewb]

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

 

[Scot E]

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.

 

[RMulhern]

It's pretty simple to divide 63 by 5!!

 

[Michael Eichele]

.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.

 

[RMulhern]

DON'T TAKE IT FOR GRANTED....that whatever scope you're using is giving the amount of movement that the maker states!

 

[trebark]

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.

 

[load]

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)

 

[LongRangeNewb]

Thanks for the help . Is there anything else i should know before sendin a few rounds down range?

 

[RMulhern]

Thanks for the help . Is there anything else i should know before sendin a few rounds down range?

Yep!

WIND IS YOUR FRIEND!!lightbulb

 

[trebark]

Thanks for the help . Is there anything else i should know before sendin a few rounds down range?

Close your eyes and mash the trigger!

Actually, relax, breathe, exhale, pause, squeeze, bang!

 

[load]

spin drift always requires left correction unless you have one of those wierd barrels then of course it doesn'tgun)