Windage for dummies

A common question I get is how to figure windage when shooting at distance. I am certainly not going to claim to be an expert in that field. Nevertheless, the Army used to have a simple formula to calculate how much windage must be adjusted, so I will share it. Also, I've done some research on common 5.56 / .223 ammo, and will share some findings with you on that, too.

Formula:

Adjustment (in MOA) = R x V
                                           C

Where
R = Range in hundreds of yards.
V = Wind Velocity
C = Constant.


Note:
The M1, M14, and M1A rifles take windage adjustments in 1 MOA increments.
In other words, 1 click = 1 MOA.

The AR15 rifle has two common types - 1 MOA adjustments and 0.5 MOA adjustments.
If your elevation knob has a "6/3" setting, then your sights are adjusted in 0.5 MOA increments.
If your elevation knob has an "8/3" setting, then like the M1 and M1A, you have 1 MOA adjustments.


.30 Caliber
For the 150-grain .30-06 and .308 (or similar), The Constant, "C," is 10

Therefore, suppose we had a range of 300 yards, a wind of 10 mph. The formula would look like this:
(3 x 10)/10 = 3.
So we would adjust the sights by 3 MOA, which is 3 clicks.


5.56 / .223
For the AR15 rifle in the traditional chambering, there are two kinds of ammo that are more popular than others among commercial ammo. Let's face it, if you are hand loading rounds for long range shooting, you don't need my advice on windage. The two most common loads are M193 clones (55-grain at 3200 fps) and M855 clones (62 grain at 3100 fps).

For 55-grain M193 clones, the C = 7.
Given our example above (300 yards, 10 mph wind), the formula would look like this:
(3 x 10)/7 =  4.3 MOA.

Since we cannot have a partial click, one would round.
An "8/3" sight would be adjusted 4 clicks.
A "6/3" sight would be adjusted 9 clicks (4.5 MOA).


For 62-grain M855 clones, the C = 9
Given our example above (300 yards, 10 mph wind), the formula would look like this:
(3 x 10)/9 =  3.3 MOA
An "8/3" sight would be adjusted 3 clicks.
A "6/3" sight would be adjusted 7 clicks.


Verification
Please verify at actual ranges with the same ammo you plan to shoot.
These approximations will put you on a 20" target up to 500 yards.
In every instance I checked, these formulas worked to within 1 MOA. 
See this ballistic calculator and double check for yourself.


Measurements used:
.30-caliber ammunition -
.420 BC
1.1" Sight height
Muzzle velocity: 2800 fps

55-gr 5.56 ammo -
.243 BC
2.5" Sight height
Muzzle velocity: 3200 fps

62-gr 5.56 ammo -
.304 BC
2.5" sight height
Muzzle velocity: 3100 fps


.