Caculating Wind Drift

[theEMP]

Hello everyone, got a question for ya'll if you can help me out. I'm trying to learn how to calculate wind drift. I have found a Army formula of
(range/100) x wind velocity / constant.
My question is how do you find out what the constant is for the rifle and load? Is there some formula for figuring it out or is it just off of range experience? I shoot a 300 win mag with 165 grain Nossler Accubonds that have a B.C. of .475 and it is has a muzzle velocity of 3200 fps. Any tips would be very helpful. Thanks.

 

[Canadian Bushman]

I personally plug in my bullet info to a ballistic calculator with a 1 mph full value wind out to about 1k yds.

That gives me a baseline bullet drift per 1mph full value wind out to 1k

Then i use the bullet drift value ( say .5 @600yds for 1mph full value wind ) times the speed of the wind, then times the wind value. And that will yeild a pretty accurate wind correction.

Heres is my cheat sheet.

 

[BrentM]

Cool

 

[theEMP]

Thanks for the help. I think I need to get out and put some rounds down range and try it out.

 

[Canadian Bushman]

If you dont have a ballistic calculator i can run your numbers for you but until you start chunking lead its all just theory

 

[BrentM]

He can make charts off the Hornady website as well. They have a nice calculator that is easy to use. I tend to copy and paste the chart into a spreadsheet and delete data I don't need. I make a couple of charts, but them back to back, then tape the whole thing in packing tape to be water proof etc. I slip this under the neoprene cheek cover on my stock. If I can't get to Shooter quick enough I pull the chart. I use 5mph wind for drift vales out to 1000 in 50 yard increments from 200 yards. If the wind is 10 I double the number, etc.

Example: at 650 yards at 5 mph drift is 1.7 MOA/9.8 inches at 3 and 9 Oclock positions. So for a 10 mph wind it would be 3.4 MOA/19.6 inches. To use the 45 degree angle you can now take the number .7 x X = Y and you hold or shoot for Y. Y should be @ 5 mph 1.2 MOA / 6.8 inches if I did it right.

Ballistics Calculator - Hornady Manufacturing, Inc

 

[ShootnMathews]

Interesting point Brent.

 

[WildRose]

He can make charts off the Hornady website as well. They have a nice calculator that is easy to use. I tend to copy and paste the chart into a spreadsheet and delete data I don't need. I make a couple of charts, but them back to back, then tape the whole thing in packing tape to be water proof etc. I slip this under the neoprene cheek cover on my stock. If I can't get to Shooter quick enough I pull the chart. I use 5mph wind for drift vales out to 1000 in 50 yard increments from 200 yards. If the wind is 10 I double the number, etc.

Example: at 650 yards at 5 mph drift is 1.7 MOA/9.8 inches at 3 and 9 Oclock positions. So for a 10 mph wind it would be 3.4 MOA/19.6 inches. To use the 45 degree angle you can now take the number .7 x X = Y and you hold or shoot for Y. Y should be @ 5 mph 1.2 MOA / 6.8 inches if I did it right.

Ballistics Calculator - Hornady Manufacturing, Inc

I use Hornady's calculator as well.

I've been doing this in my head for so long I'm not sure if I can put it to paper but I'll give it a try.

Let's start with this.

A full value wind comes from either 9:00 or 3:00. Therefore I divide 90deg by 3 = 30deg for each five minutes off of full value.

If my 500yds correction for a full value 20mph wind is 15 MOA but I only have an 11o'clock wind I just figure a 5 MOA correction and let it fly.

Or for a quicker shot I have my charts set up in inches so I can use the size of the target to calculate an even quicker windage solution.

If I'm making this shot on a white tail I'll just figure 4" from point of shoulder to the edge of the hip. If my correction is 15" I'll rough out the correction then to dividing the 48" by 15 and use the width of the shoulder blade as my correction, slide the cross hair over that far and let it fly.

There are certainly more precise ways to calculate it but for quick shots this method will definitely get the job done for you.