Quote:
Originally Posted by 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

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.