Everybody knows about ranging at a target with a laser range finder, but not everybody knows that you can range a target with a mil-dot scope. Though not as accurate it allows the shooter, once proficient, to range a target probably faster than he can get the range finder out of his pack. It also allows you in most cases to range a target farther than you could with a laser range finder. The biggest draw back however is it gets harder to range accurately the farther away the target is. So you should probably try to keep it under a 1000 yards or less depending on your rifle. Below is a example of my mil-dot scope reticle.
Notice that each mil on 10x power equals 3.6 MOA which is 3.6 inches at 100 yards and 36 inches at 1000 yards. MOA or minuet of Angle is a term used to explain a type of measuring that you will use in shooting. One MOA is always equal to the range that you are shooting. 1 MOA equals 1 inch at a 100yds, 2 inch’s at 200yds, 3 inch’s at 300yds and so forth. And 2 MOA is double the range that you shoot. 2 MOA equals 2 inch’s at 100yds, 4 inch’s at 200yds, 6 inch’s at 300yds. Now that you understand MOA a little bit lets say you are aiming at a target that 36 inches tall and it takes two mil-dots to cover the 36 inch target. This is how it works 36 inches equals 1 yard so you take 1 yard times 1000 divided by the number of mils (2) equals 500 yards. Another example is a 24 inch target (.667yds) that takes only 0.5 mils. Now take .667yds x 1,000 = 667 / .05 = 1,333 yards. Or you can take the size in inches times 27.778 and then divide by the number of mils and that will give you the range as well. Its really quite easy to do, the best thing to do is to make a chart ahead of time and it just so happens that I took the liberty to do this for you which I included below.
Here is also a game that is very good practice that includes mill-dot ranging: Long Rang Shooting Game