With the growing popularity in the shooting world of Mil-Dot reticles in rifle scopes, I thought I would take a little time to explain what they are and how they work, as well as some differences in the commonly available models on the market today. The mil-dot reticle is primarily used as a range finder. The dots and spacing are of known sizes and ratios and can quickly be used to estimate the range to a known sized target.
...

One of the most frequently asked questions we see on the forum is in regards to scope rings and bases, more specifically what combination of the two will permit clearance of a scope with a specific size objective lens. Obviously with the limitless number of possible base/ring combinations available this can be a difficult question to answer, but the information provided below should allow you to determine exactly how much clearance is necessary for the scope you have selected to mount on your rifle.
...