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Wind Drift Formula?

18K views 10 replies 8 participants last post by  jasonk 
#1 ·
Looking for a simple wind drift formula for shooting deer across bean fields in fairly stiff breezes.

If I recall correctly, if the wind direction was perpendicular to the path of the bullet, you could calculate wind drift as follows:

WIND DRIFT IN FEET = [AVERAGE WIND SPEED IN FEET PER SECOND] x [TIME, IN SECONDS, OF BULLET FLIGHT FROM MUZZLE TO TARGET]

For example, if the wind was blowing at a 90° angle to the path of the bullet to the target at a speed of 5 feet per second and it took 1/10 of a second for the bullet to travel from the muzzle to the target, then the wind drift could be calculated as:

[5 feet/second] x [1/10 second] = 5/10 feet = 1/2 foot = 6 inches

Am I anywhere near correct with any of this?

Thanks,

Pike
 
#2 ·
Crude

I read a simple idea on how to hold for wind. It was a rough guess to get you close.

Here it is.
For every 10 mph crosswind, you square the yards.

Example #1. 200 yards with a 10mph crosswind. 2X2= 4 inches of wind drift. If it were a 20mph wind(flags straight out from the pole) you would double that, so it would be 8 inches.

Example # 2 300 yards with a 10mph crosswind. 3X3=9 inches of drift. 20mph would be 18 inches.

This was a simple plan made up to help get a shooter closer on target without detailed information or equipment.
 
#5 ·
I use mil-dots when hunting across bean-fileds. I first figure the furthest range across the wide open space and then look at the mirage/leaves blowing and figure the wind speed in miles per hour. Then I calculate the range divided by 100 multiplied bt the wind speed and divide by 20. That figure gives me the most extreme windage required for a one shot hit at a standing deer to the furthest reach of the field. Its really an easy problem when sitting there observing the conditions for a half hour. Figuring the wind speed via the mirage or blades/leaves blowing is easy as well. My advice only pertains to waiting in the same position with the wind blowing from near the same direction at a somewhat constant speed. My method only allows me to figure the MOA needed to adjust at the furtherest distance in the field. Your sight's adjustments will require you to understand MOA at different ranges. The method I described was taught to me years ago and I find it easy and quick. I do use a calculator as I have some time while watching the conditions. If bambi appears when I'm not fully dialed I don't worry too much as long as Mr Mossyhorns is within 500 meters. After all...I am only trying to hit an 8 inch vital area and most .308's will do that at 500 meters with a rifle zeroed at 100yds in light winds. The problem comes to novice long-range shooters when they over-compensate bullet drop and drift at distance. If you look at a ballistics chart it appears the .308 drifts/drops a lot in a ten MPH cross wind...and it does. You must also figure the value of the wind. The direction the wind blows across the rifle has more of an effect than getting the elevation right when shooting at an 8 inch area.
 
#7 ·
Thanks, guys.

I'm not going to be using my M1A, so the M1A-specific instructions aren't helping me too much...how many MOA is one click of windage on the M14 sight? (I'm eyeballing the windage correction on the peep sight on my M98 30-06...)
 
#11 ·
You must know your sights first. You can know MOA at different ranges easily...but that doesn't help if you don't know the MOA value of your sights. I have two M1A's one has a full minute per click and the other has 1/2 minute from the rear sight for windage. Again you must know your sights before you worry about MOA's at different distances.
 
#8 ·
"...how many MOA is one click of windage on the M14 sight?"
Basic formula is
1click=1MOA at 100yds
1click=1MOA at 200yds

MOA at 100 is about one inch
MOA at 200 is about 2 inches
MOA at 300 is about 3inches
MOA at 600 is about 6inches
I think.......
 
#9 ·
I use the following thumbrule.

For 600yds:
2MPH full value wind is 1minute

For 300yds:
Divide the above rule in half

For 200yds:
Hat blows off = 1minute (maybe two depending on the fit of the hat)


The old formula in the manuals from the M1 and M1903 days is:
Minutes = MPH wind * Range (in hundreds of yds) / 10
 
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