Ryan Cleckner [above] was a special operations sniper team leader in the US Army’s 1st Ranger Bn (75th) and a sniper instructor with multiple combat deployments. Click here to pre-order his book Long Range Shooting Handbook- A Beginner’s Guide to Precision Rifle Shooting from Amazon. Here’s chapter 18 on estimating and adjusting for target distance . . .
I strongly believe in learning how to shoot a rifle with iron sights before putting glass on your gun. It should come as no surprise that I also encourage learning and practicing to estimate a target’s distance with angular measurements — using the Mil or MOA marks in a scope — before buying or using a laser range finder. So let’s get to it!
18.1 Angular Measurements (“Milling”)
There’s an inverse relationship between how big an object appears and how far away it is. As the distance to an object increases, the size of the object appears to decrease. Imagine a target at 100 yds as a starting point. See Figure 18.1-1.
If you moved that target to half the distance (50 yds) from your vantage point, it would appear twice as large. Likewise, if you moved the 100 yd target twice …Read the Rest
Source:: Truth About Guns