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Sighting in a rifle scope is something that needs to be done whenever we make a change. Whether that change is an ammunition or load change, or you have installed a completely new scope on to the rifle. Knowing how to zero a scope is an important part of the sighting in process. In this article, I will outline the whole procedure for you.

How to Sight in a New Scope

If the rifle and scope set up are new and have never been fired together. Then it is a good idea to do a bench set up first. The tool I prefer to use for the initial setup is a boresighter, (not the laser type). The boresight uses different sized pilots that fit the specific caliber of the barrel. Once the correct size pilot has been installed you just attach the lens assembly to the pilot and look through the scope.

Boresighter being used to set up the scope adjustments
Using a Boresighter to set up the initial scope settings. This will get you on the paper but will still need to be fine tuned at the range

When you look through the scope into the bore sighter lens on the end of the barrel you will see a grid. All you have to do is adjust the crosshairs so that they are in the center of the grid. Normally I will set my crosshairs a little low on the grid by a couple of lines as this seems to work the best. Remember this is just to get us on the target when we go to the range.

Scope mounting errors

Although in this article we are not going into the mounting procedure of the scope it is something you need to consider. One of the biggest issues that I run into is loose scope mounts and loose rings. So, make sure the scope mounts are torqued to 65 Inch pounds and the rings at 25-35 inch-pounds. If you are not sure of the correct torque, then contact the manufacturer for more information.

checking scope torque, how to sight in a scope
Always check that scope mounts are tight on a regular basis

It is a good practice to routinely check your existing scope mounts. Scope mounts especially on large caliber rifles can and do come loose.

Ammunition and its effects on scope zero

Differences in ammunition will make a difference to the zero of the rifle. At close ranges, the effects are usually going to be minimal. However, as you stretch out to longer distances, different bullets traveling at different speeds will drop different amounts. This means that if we make a change from the original cartridge that we used to sight in the rifle, then we should repeat the sighting-in procedure.

load development showing different charge weights
Different powder charge weights will affect velocity and POI. The picture above shows a load development where the rounds are using different powder charges. The weight of the charge is written on each row

Other elements that can affect the rifle zero

Another point to keep in mind is that the location that we plan on shooting at. If the rifle is zeroed at our local range that is roughly at sea level, but our hunting trip is going to take place at a 6000′ elevation then our zero will need to be adjusted again. This is because the bullet will travel faster at a higher elevation due to the atmosphere being thinner. This is turn will change the POI, (point of impact).

It is Ok to do a rough zero at your home range, just make sure that you allow a little extra time to re-adjust your zero once you get to where the rifle is going to be used. Atmospheric conditions will also play a part in zero settings so if possible, it is always best to zero the rifle where it will be used.

How to zero a scope at the range

Now that you have the scope mounted and tight and you have chosen the perfect bullet for you its time to get the scope dialed in. If you have used a bore sighter then you can most likely just set out your target at the 100 Meter/yard point. However, if you did not have access to a boresight tool then it is a good idea to start the sighting process at 25 meters/yards.

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Sighting in at 25 yards for a 100 yard zero

Although using a 25-yard starting point is a great way to get on target it is not indicative of a true 100 yard zero. It seems that a lot of people seem to think that a 25-yard zero will be a perfect zero at 100 yards. This is just not the case. If the rifle is sighted in at 25 yards, then it will most likely be high at 100 yards due to the sight and barrel height difference.

If you must start at 25 yards set the POI to be about 1” to 2.5” low depending on the sight height as measured from the centerline of the barrel to the centerline of the scope. This will get you close at 100 meters/yards.

Barrel to scope height relationship
Measuring the scope centerline in relation to the barrel centerline. This scope is approximately 2.5″ high

Sighting in a 100 yards

First shots on target
The first shot was approximately 1 Mil high and 1 Mil left, adjusting the scope brought the 2nd shot down and right. A couple more quick adjustments brought the rifle on target
Need to understand the difference between FFP and SFP scopes? Read Here

Checking the Scopes repeatability

Once the scope has been sighted into your rifle it is time to verify the operation of the scope. To do this we are going to shoot a box pattern on the target. This will do two things for us; it will verify that the scope’s adjustments match the dial indications. It will also help get the grease used in the scope at assembly to circulate throughout the scope.

Shooting the Box

Watch our video on how to zero your scope and then shooting the box

Analyzing the results of shooting the box

Now we want to check the target and see how well the scope performed. Use a tape measure and measure the distance from the aiming point to the center of your group. It should equal 1 Mil, (30 centimeters or 12”). The group should also be level with the first group. 

Measure all of your group’s checking to make sure that the box corners are square and consistent with each other. If your shots are not aligned correctly there can be several reasons why.

Shooting the box scope checking drill
Target set up with four targets spaced at 1 mil for shooting the box drill. The target in the center is for an elevation drill.

How to zero a scope: Fault Diagnosis

Shot groups not level:

 This is when your shot groups are landing higher or lower than the first group when you have adjusted right. This is most likely caused by the scope not being correctly leveled to the rifle. This will result in slight elevation changes when adjusting windage. To correct for this issue set up and level the rifle in a gun vise. Then check and adjust the scope level in relationship to the rifle.

If the scope and rifle are leveled re-check that you are holding the rifle level when firing. Using a scope mounted level can help you with this.

Lastly, if both of the above causes are not the issue it is most likely an internal scope issue. You should replace or return the scope to the manufacturer to have it repaired.

Shot groups not vertical

Shot groups that are not perpendicular to the first group are usually a result of the scope and rifle not being level. Generally, the shot group will also not be level with the first group either. Perform the same checks as above and return or replace the scope if necessary.

The shot group did not move the correct amount

A shot group that did not move the correct distance will be a result of an internal calibration error with the sight. There are two ways to deal with this, the first would be to replace the sight. The second would be to just take it into consideration when mapping out the ballistics for the rifle/ammunition combination you are using. This would only be a viable solution if the sight is repeatable and reliable in all other facets of its operation.

Shot groups are not regular distances

Groups that do not land at regular distances from each other or changing elevation results in a windage change will typically equal a bad scope. This indicates that the scope is worn out internally. Or it is just a poor quality. Replace the scope and re-zero.

How to zero your rifle
Measuring group spacing to check for scope calibration

The scope will not return to its starting point

If your group does not return to the starting point on either elevation or windage then that is indicating excessive backlash in the scopes adjustment system. You will need to return to the manufacturer or replace the scope.

Conclusion of how to zero a scope

Now you should be set to go and ready to shoot. Your scope should be correctly sighted into your rifle at a 100 meter/yard zero. Now all that is left is to shoot to the distances you plan on using the rifle for. Then update your Dope book with the ballistics. Remember scopes are a precision device, but they are only as good as the shooter behind them. Remember to practice good shooting techniques and check that the optic is tight to the rifle regularly.

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