For hunters, the rifle is their most important tool. Some spend hundreds on accessories just so that their rifle is the best, so that they know that that a bullet will go precisely where they aim it. This means that barrel has been properly cleaned, and that every piece works as it should. However, the piece that is most likely to cause the most problems is the scope, given that there is a boot that may not quite fit right and optics that must be cut right. For this reason it is imperative that a hunter learn how to sight in a rifle scope.
Before you begin, it is important to do some basically troubleshooting. It is important to make sure that the scope fits right and tight in the boot; if it fits properly it moves as part of the rifle with no wiggle room. There should also be no cracks in the housing that can let in water vapor or possibly break the scope when it is fired. The lenses also need to be inspected to make sure that they have no smudges or other imperfections; they should be cleaned whenever the scope has been used. This means that the scope should be left in the case unless it is actually being used.
You are going to need a chronograph as well as twenty to forty rounds of ammunition. It can only help to have information as accurate as possible, and the more information you have the more accurate your scope will be. The chronograph needs to measure the speed of the bullet, and you need enough information to verify the numbers you obtain. The ammunition should be of the same time that you plan to use, and preferably from the same lot. While that is easy enough for those that purchase their ammunition, handloaders should do what they can to insure that all of the ammunition has been loaded the same and that the information has been tracked so as to insure a consistent load.
You will also need to either print out the appropriate tables, or have access to some sort of software that will allow you to keep track of all of the information. You should also know how fast your particular combination of rifle and ammunition should go, usually expressed as a range. So armed you can head out to the range. You may need to make two trips: One to gather information and another to actually sight in. While it may seem a little pointless to gather this information, it is important because you want to make sure that your rifle is performing not consistently but within specifications; if the rifle is not performing within specifications there may be other issues to look at, and if it is not performing consistently it can be difficult to actually sight in.
The first shots should be fired at a target just 25 yards away. For information-gathering purposes, you should not need to expend more than 20-30 rounds; the more information the better, but there is an effective limit to how much information is useful. Once you have all of information, make sure that the ammunition is performing with expectations before actually sighting in. Expect a few shots that are outside of the expected range, especially if you are using handloaded ammunition, but just confirm that the ammunition performing reasonably consistently.
There are two basic ways to sight in. The first involves shooting three shots in a spread that a small saucer can cover, or a circle about 4 inches in diameter Adjust the scope, based on the center of the grouping, towards the center of the target and fire three shots again. Adjust if necessary. Fire either one more time to confirm that the modifications worked, or until you have two groupings that cover the same pattern. Depending on how well you have maintained your scope, this can use six to nine rounds. If you wish to fine tune things a bit, repeat this for additional ranges, such as a 50-yard or even 100-yard target. Once it has been sighted in there is absolutely no reason to get in some shooting practice, especially for those shoot at more extreme ranges.
There is a slicker way of doing this that uses less ammunition. Fire off one shot, but do not chamber another round. Instead immobilize the weapon in the precise place that you fired from, and adjust the sites so that the sites on the scope move to adjust for the difference between where it actually shot and where it was intended to hit. Fire again and repeat until the round hits where you want it to hit. With a little bit of luck and some serious skill, you should be able to site in within a few rounds. Of course, you should try it at some longer ranges just to confirm that the scope is sighted in properly.
Downtime between hunts should be spent looking for ways to improve aim, as well as pushing the rifle to its limits. It is important to know the limits of the rifle, including the scope. If the scope has any special features these should also be explored to see if there are any issues with them and if they make aiming easier or harder. Suffice to say that the scope should also be sighted in for each of the special features so that there are no surprises in the field, and that adjustments can be made as needed and quickly.
The cost of the scope is not important as long as it works. Too many hunters get wrapped up in buying the most expensive accessories that they can for their rifles, without realizing that cot does not always equate to effectiveness; sometimes a $50 scope is actually more effective than one that cost several hundred dollars. It is thus important to pay attention to reviews and discussion boards to find the best scope for your rifle, and that is more important than spending too much on something that does not quite work.