The basic Mil Dot reticle uses a series of dots along the crosshairs of the scope. These dots have a defined relationship useful for estimating the range once you understand how to use them.
Let’s define MOA “minute of angle.” There are 360 degrees in a circle. When we divide one degree into 60 parts, we have an MOA.
Since 100 yards is a common range for sighting in a rifle, talk commonly turns to how a rifle will group at 100 yards. Often, the talk turns to whether or not a rifle can shoot MOA groups. This normally means that the rifle can keep the group an inch or less at 100 yards. MOA groups are often referenced. This normally means that the rifle can keep the group 1 inch or less at 100 yards. In actual fact, 1 MOA at 100 yards is 1.047 inches, with the assumption 1 inch is good enough (virtually no one can hold tighter than 0.047 inches anyway). This is found by multiplying the range by the sine of the angle. Using the range in inches (100 yards = 3,600 inches) times the sine of 1/60 of a degree (1 MOA) gives us the 1.047 inches at 100 yards. I find it easy to use a calculator.
If 1 MOA is a bit over 1 inch at 100 yards, how large is 1 Mil at 100 yards? Let’s define a Mil. Some think that “mil” comes from “military,” but that is not the case.
There are 2π (2 times Pi) radians in a circle, corresponding to the 360º to which we are more accustomed. Dividing 360 by 2π gives us 57.3º per radian. That’s pretty big, but that’s radians, not milliradians. Milliradians are what we term a Mil. A milliradian is 1/1000 of a radian, so 1 Mil is 0.057º, giving 1 Mil at 100 yards covering 3.6 inches. Large compared to1 MOA, but useful.
A Mil Dot reticle has specific relationships between the dots and the spacing of the dots. Similar reticles could be made using MOA, but 1 MOA dot spacing would be crowded, so what interval would be used? Since the Mil is a fixed, but usable spacing, it takes the potential variability of how far is it between dots and fixes it with one known value for any Mil Dot reticle. Because of this precise spacing, the Mil Dot reticle is very useful for range estimation.
Planning the First Shot
As an example, assume you’re antelope hunting in a location overlooking grazing land and there’s a stock-watering tank in view. Your laser range finder is not working. You do know the side of the tank is 3 feet high. Looking through the scope, you note that the tank side exactly matches 1 Mil. The rule is to multiply the actual size viewed by 1000 and divide by the Mil value, or: Actual target size (in yards) x 1000 / # Mils = Range (in yards).
With a 3 foot tank side, subtending 1 Mil, we have 1 yard x 1000 / 1 mil = 1000 yards distance to the stock tank. Okay, that’s an easy one. What if the side of the stock tank subtended 1.5 Mils? Like this; 1 yard x 1000 / 1.5 = 666 yards to the water tank. If you don’t have a calculator, think of the 1.5 as 3 /2, giving 2000 / 3 = 666.
Moving to a military application, think about a situation where you are watching a town for hostile personnel. You know the doorways are 6.5 feet (2.2 yards) high. You’re out far to avoid detection, armed with a .50 BMG rifle. The doorway comes out as 2 Mils in the scope, giving a range of 1100 yards. (2.2 x 1000/2 = 1100).
A feature of the mil is that it works with either yards or meters. If the known target size is in meters, the resultant range is in meters as well.
The 50 BMG was originally conceived as an anti-materiel round, not anti-personnel. That usually means bigger targets. The Mil Dot reticle helps us for distant targets by allowing good range estimation.
Commonly, once you have a good range value, you will dial in the necessary change in elevation in the scope. This allows using the center of the crosshair normally. There may be times where it is easier to hold over or under on the target. With the Mil Dot reticle, the dots give references that provide more than a guess at how much you are holding over the target.
As part of your homework, you developed trajectory tables for the bullet you are shooting. Thinking of that 1100-yard shot of the military situation, if the rifle is sighted zero at 1000 yards, the trajectory table shows that the bullet will be almost 45 inches low at 1100 yards. One mil, at 1100 yards, will span 1.1 yards, or almost 40 inches. The dot itself covers 0.2 mil, corresponding to about 8 inches at 1100 yards. Holding over the target by 1 mil, plus half of a dot (0.1 mil) gives a ready reference for hold over, compensating for the bullet drop when making the shot.
Windage With Mil Dots
Mil Dots can even be used to allow for the wind. Shooting with blowing wind, always introduces unknown factors. To calculate the effect of the wind, assume that the wind has constant velocity and is the same over the entire range the bullet will travel. It doesn’t often work that way, but understanding the effect of the wind on the bullet under the constant conditions will give insights to what’s happening in the field.
Assume a crosswind velocity of 5 mph, and that it is uniform over the range. From the ballistic table, we see that a 5 mph wind, over 1100 yards, will move the bullet almost 24 inches to the side. As we previously saw, 1 mil at 1100 yards covers some 40 inches. So half a mil will cover 20 inches. Add half a dot and we can hold into the wind at barely over half a mil (0.6 mil) and thereby compensate for the wind.
With a standard crosshair reticle, we only have the crosshair wire, and there is no good reference as to how far along the wire we need to hold off to make the hit. The Mil Dots contribute useful references to allow better shooting.
Holding into the wind is very similar to leading a moving target. They are always difficult. Moving targets at long ranges add greatly to the problem of getting hits. Military situations may require taking a shot at a moving target.
Understanding and using a Mil Dot can contribute to a successful shot. The amount of lead needed is dependent on the target speed. High velocity target speed means passing on the shot. If you can’t keep the target in the scope view, there is little or no likelihood of holding the needed lead.
If the target is moving directly across your line of fire, it is moving some 88 fps if going 5 mph. Staying with the 1100 yard range, we know that 1 mil corresponds to 40 inches, so leading the target by 2 mils, plus a dot diameter will give a good lead. As with an accurate range estimation and knowledge of your trajectory, it’s crucial to make an accurate determination, or estimation of the target velocity.
The Mil Dot reticle has a great deal of utility over a plain crosshair reticle. There are others that offer similar features of the Mil Dot, and they may do better in some situations. The Mil Dot is widely found and easy to understand and it has the added advantage of being the same everywhere.
Note that many Mil Dot scopes are variable power. The Mil Dot is geared to a specific magnification for that scope. Be certain what magnification corresponds to the Mil Dot. Normally it is the highest magnification.
If you’re in the market for a scope, I would recommend a Mil. As with any shooting, you must use what works best for you. The Mil Dot system has worked well for many riflemen for many years and it can be a valuable tool for you, too.