Re: Mil Dots?
You definitely need some way to range your target if working with targets at unknown distances (ie, anytime you aren't on a known distance range).
To a point you can "eyeball" the range, but obviously that is error prone, and at some distance (depending on the ballistics of your load, your skill at eyeball ranging, luck, etc), it will be too inaccurate for whatever level of precision it is that you require.
With practice, you can get more accurate distances by using a ranging reticle based on some unit of angular measurement (those units are usually MILs, true MOA [minute of angle], or IPHY [1 inch at 100 yards]. Based on the apparent size of the target in relation to the reticle markings, and the size of the target, you can calculate the range to the target (it's basically a ratio calculation combined with unit conversions -- the exact formula will depend on reticle type, units of measurement you are using, etc). Again, there is a point, depending the true range to the target, conditions, your skill, etc where this method will no longer be accurate enough for whatever level of precision your require.
You should be aware of the difference between first and second focal plane reticles. A second focal plane reticle is calibrated at a certain zoom power, so needs to be used at that power on a variable power scope for accurate ranging (you can also use math and range at various multiples of that power setting -- but that adds an extra layer of complexity). A first focal plane reticle gets larger/smaller along with the zoom of the scope, so the angular markings on the reticle are always "correct" at any power. The downside is that the scope markings get thinner/thicker as you zoom. For tactical style shooting first focal plane reticles (FFP) are very popular because of their versatility.
The other thing that a reticle helps with is accurately correcting for misses (you can see with the reticle exactly how much you need to correct for the next shot), and for "hold-offs", ie, correcting for wind/elevation by using the reticle markings instead of dialing on the knobs, which can be faster -- especially for follow up shots, changing wind, or multiple target engagements. It is a very good idea to get target knobs that have 'clicks' based on the same angular units as your reticle markings so that can easily go between reticle markings and "clicks". For example, Mil based reticle with .1 MIL clicks, or MOA based reticle with 1/4 MOA clicks.
Of course, there is technology that makes ranging extremely easy and accurate (if it works!). A good laser range finder (such as the Swaro Laser Guide) is faster and more accurate than reticle ranging -- but even if you can always range with the laser, reticle markings are still useful for corrections and hold-offs.
Hope that helps.
-Matt
