Moving to long range hunting/shooting from conventional hunting requires the the distance(s) be know BEFORE the shot. Why it this important and are those distances real? You've no doubt read some of the distances that are stated here for shots, in nearly all the cases the distances are real. The method we use to make these shots requires that the distances be known to within certain tolerances, the further the distance the less error allowed. We NEED to know the distance before the shot because we adjust the scope (in most cases) or use calibrated reticles. If the shot is to be at 600 yards we'll adjust the scope for the 600 yard distance, check the wind (we'll talk wind later) check the target area and when ready, fire the shot. If we maintain proper form and follow through we'll have a hit, simple as shooting 100 yards (nearly). For me, long range shooting is not about shooting a miss, it's all about making hits. The distance MUST therefor be KNOWN before the shot. What methods are used to get these known distances? Laser range finders, they do have limitations but are a tool that must be understood to be used properly. Eyesafe commercial versions are available for ranges (under ideal situations) to 2000 yards. Military versions can determine ranges to greater than 15 miles (I don't shoot that far yet ) Optical coincidence rangefinders, split image optical rangefinders. These rangefinders use a long tube to house mirrors and lenses that require the operator to align two images of a single object. Once the image has been matched the distance can be read from the alignment dial. There are inexpensive devices listed in many hunting catalogs and there are the better, more useful military models. Premeasured areas work well to a certain point.. distance across a 40 acre (square) field is about 440 yards. Use of a GPS for distance determination is available. The GPS can report distances in Universal Transverse Mercator (UTM) mode which is distances in meters. Basic calculation then becomes, subtract one Easting value from the other and the Northing value for the other. Use the two difference values as "A" and "B" in the Pythagorean theorum and you'll have the distance "C", in meters, to the target. How much error is acceptable? The further the shot, the less error allowed. The greater the ballistic arc of the round being fired, the less error allowed. The smaller the target, the less error. A quick number, would probably be 25 yards plus or minus to distances of about 600 yards and a larger 24" depth target. Past that you'll need to be closer on the distance. At a mile, 5 yards plus or minus gets to be a fair amount of drop difference.