So many scopes on the market today are outfitted with a Mil Dot reticle, but are people using them to their full potential? The answer is probably “no.”
The Mil Dot reticle can be used for multiple purposes that includes range estimation, shooting using “hold overs,” compensating for the wind, leading a moving target, and probably a few others that I’ve failed to mention. But we’ll limit this guide to using the reticle for range estimation.
First or second focal plane?
Before using it for estimating range a key feature must be recognized first. Does the scope have a first or second focal plane? Without getting into all the details and differences between the two, there is a quick way to tell.
In a scope in the first focal plane — sometimes called the “front” focal plane — the reticle grows in size along with the target. Reason being he reticle is in front of the magnifying lens. And in scopes in the second focal plane, the reticle stays the same size as the scope magnifies. Reason being, the reticle is behind (closer to the eye) than the magnifying lens.
Knowing if the scope is in first or second focal plane is very important for using the reticle for range estimation because the differences make big changes. For example, in a first focal plane, the reticle at 5X one mil covering 3.5 inches on target will increase in size along with the target, so when zoomed 10X, it would still appear to cover the same 3.5 inches. But if a second focal plane scope was used, the reticle would appear to cover 7 inches at 5X and when zoomed to 10X, the target would appear to enlarge while the reticle remained the same and then would appear to only cover 3.5 inches.
Which is better? Well that’s completely different article, however, there are good arguments for both sides. It all depends on what you are using the optic for. The important thing to take away is that a first focal plane scope can be used for range estimation at any magnification setting whereas a second focal plane scope can only be used at one particular setting — typically the scope’s maximum setting.
Using the right formula
There are a couple of different formulas used in range estimation using a Mil Dot reticle, and instead of explaining “how” each of them works, I will simply explain the formulas. Although they may appear complicated on paper, they are very easy if you use a calculator.
1. Take the size of target in inches and divide it by 36, then multiply by 1,000, and then divide the total by how many Mils the target reads inside the scope. That answer will be the range to the target in yards.
Formula 1: (Size of target in inches/36) x 1,000) / Mils = Range in yards
For example, take the size of a stop sign from edge to edge, which is 30 inches. The first step is to take that 30 and divide it by 36, which equals 0.833333, and then multiply the figure by 1,000, to get 833.3333.
The second step is to divide the answer to the first step by however many mils the stop sign subtends in the reticle (It’s best to break the reticle into the smallest practical increment; I’ve found that estimating the reticle into tenths works well). If the stop sign covers 2.8 mils then the sign would be approximately 297 yards away.
Practice equation: 30 / 36 = 0.83333; then 0.83333 x 1,000 = 833.333; and then 833.333 / 2.8 = 297
2. I’ve also found another formula that works well for estimating range. It’s involves taking the size of the target in inches and multiplying it by 27.78, and then dividing by the number of Mils the object subtends in the scope.
Formula 2: (Size of target in inches x 27.78) / Mils = Range in yards
For example, take that same 30-inch sign. The first step is to multiply the size of the target by 27.78, which equals 834. Since the sign covers 2.8 mils in the scope, the sign is then 297 yards away.
Practice equation: 30 x 27.78 = 834; then 834 / 2.8 = 297
Before putting it to practical use
I’m by no means a math genius, but I do know that these formulas work. There are however some key considerations to keep in mind. If you’re not square to a target that you’re trying to Mil, the target will seem smaller than it’s true size and will appear farther away. Try to get as close to a 90 degree angle as possible.
Also, mirage distorts the targets edges and can make range estimation a bit tricky. The key to it, like most things, is practice! Take a laser range finder out with you to the range. Set some targets out and use your Mil Dot reticle, formulate a firing solution and then cross check it with the laser range finder. You’ll be surprised how useful those little dots in your reticle can be!
Source Article from http://www.guns.com/2015/04/23/using-a-mil-dot-reticle-for-range-estimation/