What Do the Numbers Mean on a Rifle Scope? – Guide to Scope Numbers
In order to improve your shooting over long distances, you will need to understand how a rifle scope works. The scope is arguably the most important component of your rifle as it helps the shooter to locate, aim, and hit targets at distances that are outside your normal range of vision. Your naked eye can’t clearly see targets out in ranges of hundreds of feet.
The scope works by magnifying images that are very far away and aligning your aim to the image projected through the scope. There are certain numbers on the scope’s dials and knobs that are important to understand as they help the shooter identify how far and at what angle the target is located.
In this post, we will take a detailed look at the scope’s numbers to help shooters improve their rifle scope adjustment and long-range shooting. Without further ado, let’s figure out what the numbers on a rifle scope mean!
What Numbers are on the Scope?
The numbers on a rifle scope may look a bit confusing at first, but they are easy to read once you understand how they work. Let’s look at a few examples from a mid-range rifle scope.
Suppose you are using a mid-range variable power scope, and a number is written on it, 3 – 9 x 40 mm. This number shows three things. The 3 is the minimum rifle scope magnification, the 9 is its maximum scope magnification and the 40 mm represents the diameter of the objective lens. So, in this example, you have a scope magnification range from 3 to 9x.
The first two numbers show the scope magnification range. Since the number runs from 3 to 9, it shows that the scope can be zoomed between the range of 3x and 9x magnification.
Variable power riflescopes have the scope magnification range as the first two numbers as mentioned above. You have something like 3-9, 4-16, 5-25, etc. signifying the magnification range This also gives you an indication of the zoom range of the scope. A lower power scope, for example, 3-9 has a zoom range of 3x (9 divided by 3). A higher power scope might be a 5-25x which has a zoom range of 5x. Lately, variable magnification power scopes with zoom ranges of 10x have started to enter the market. Such a variable magnification power rifle scope, for example, one with a 1-10x magnification range allows covering a wide range of shooting and hunting scenarios in one scope.
This is true for rifle scopes with adjustable zoom and variable magnification range. A fixed power scope will only show a number like 6 x 45, where the first number shows the fixed magnification of 6 and the second number shows the diameter of the lens – What is the Rule for Rifle Scope Magnification vs Distance?.
Size of the Objective Lens
Larger lenses with a bigger diameter are usually better than smaller lenses. A larger objective lens allows more light to come into the rifle scope and makes it easier to focus. It makes for a much brighter and clearer image especially when you are shooting in low light conditions such as cloudy weather or dusk.
Generally, rifle scope lenses are smaller than the lenses you would find on binoculars. This is because binoculars are designed to let you see as far as they might allow, while rifle scopes only let you see as far as the shooting range of the rifle. Designing rifle scopes with bigger lenses does not serve any purpose if your rifle can only shoot at a distance of 600 yards.
Your rifle’s scope also does not need an objective lens as big as a pair of binoculars because you will mostly be zooming in on a single target and don’t need to view a wide area through the scope. The spotting scope, on the contrary, needs to allow as much light into the binoculars as possible to let you see a wider field clearly when scouting for deer during a hunt.
Another reason why rifle scopes are smaller is that they must be fitted on the rifle and carried around. If the scope lens gets bigger, it also gets heavier and the shooter may find it difficult to balance the gun due to the scope’s heavy weight.
Lastly, if you use a rifle scope with a large objective lens diameter you also have to have a rifle and mounts that support such a large scope. If your scope features a 56mm objective lens then you need mounts and rings that work with such a large size!
How Do You Calculate the Zoom Range of a Scope?
The effectively usable zooming range of your rifle scope is largely affected by the presence of sunlight in the area. Your scope might have a zoom range and magnification power of 5-25x but if there’s not enough light around you then you’ll not be able to get a clear sight picture at probably anything above the minimum magnification of 5x.
The clarity and brightness of the image are also affected by the glass quality and its finishing processes. Make sure to get a scope where the lens has a coating that improves light transmission and reduces the chance of reflection or glare in sunny conditions.
There are two main lenses on the scope. The lens at the back that is closer to your eye is called the ocular lens. The lens at the front, which is the farthest from your eye, is called the objective lens. If you observe the ocular lens from about a foot’s distance, you will see a beam of light. This beam shows how much light is being transmitted to your naked eye. It gets sharper when you turn the magnification down.
Exit Pupil and Magnification
The exit pupil on a scope can be calculated by dividing the diameter of the objective lens by the level of scope magnification. If you are using a scope that is 4 – 7 x 60 mm, you can calculate the exit pupil at different magnifications as follows (Here’s a more detailed post on how the exit pupil diameter impacts your target!).
Exit pupil at magnification of 4 = 60 / 4 = 15 mm
Exit pupil at magnification of 5 = 60 / 5 = 12 mm
Exit pupil at magnification of 6 = 60 / 6 = 10 mm
Exit pupil at magnification of 7 = 60 / 7 = 8.57 mm
The pupil on the human eye can only expand to a maximum of around 8 mm at pretty much complete darkness. If you are shooting during the day, the glare from the environment will cause your pupils to shrink. Your eye will not be able to see the full sight picture created by the 60 mm lens at 4x magnification.
Other Important Numbers on the Scope
The scope also has a variety of other important numbers apart from the lens size and magnification. These can be adjusted to improve the aiming accuracy of the rifle scope.
The tube diameter is also quite important to consider. The tube’s diameter helps you select the rings for fitting the scope onto the rifle. You won’t find the diameter of the tube written on the scope, but it is generally present on the box or in the manual.
There are two common sizes in scope tubes these days with a third one getting more commonly available. The 30 mm tube is standard. These tubes allow light to pass through in a wider area, making them useful for a larger range of elevation adjustment and higher resolution on rifle scopes. They also tend to be more expensive – Best Lever Action30 30 Rifle Scope
The second variety is the 1-inch tube which is both lighter and ideal for mid-range shooting. Scopes with this smaller tube diameter are typically cheaper.
More and more top-end scopes nowadays come with a 34 mm scope tube. These are usually high-end scopes for long-range shooting.
Field of View
A human’s normal field of vision is around a 210 degrees horizontal arc in front of your naked eye. When you begin to focus on an object to identify its features, the field of view gets smaller. Scopes work in a similar fashion. When you focus it out on your target at a distance, the field of view gets smaller.
Generally, most scopes list a field of view parameter at different ranges so that you can gauge the difference between them. Bigger lenses allow a wider field of view than smaller lenses.
A bigger FOV is better for acquiring targets in an area or following moving targets. Therefore, hunters prefer scopes with a larger FOV.
You can also use a pair of binoculars or something like a spotting scope which will have a much higher FOV than a rifle scope. These scopes have a wider field at a lower range which becomes narrower when you zoom in. This feature is designed to spot objects at a distance before you zone in on them with the rifle to make the shot – What is a Rifle Scope Inclinometer?
Elevation and Windage Adjustment
The scope’s windage and elevation determine how much you can adjust the reticle to the left and right or the up and down position on a rifle. The adjustments are typically given in MOA or MRAD and in some cases in mm.
A rifle with a windage specification of 2.5 m / 100 m means that you can adjust the reticle 1.25 m to the right or 1.25 m to the left for a target that is at a distance of 100 m. Windage range is generally specified in MRAD or MOA.
The reading scale for elevation adjustment is similar. If the scope comes with an elevation adjustment of 2 m / 100 m, then the reticle can be adjusted 1 m up or 1 m down for a distance of 100 meters – What is Holdover in Shooting?
The minute of angle, or MOA, is used in shooting over very long distances to measure the average point of impact of a bullet. It determines how much your bullet deviates over a given distance and is measured in inches.
Suppose you shoot your rifle 5 times into a 100-yard target and every bullet hits within a one-inch circle that you have drawn on the target. You could say that your rifle is at a 1 MOA. If you were shooting at a target that is 200 yards away and bullets hit within a 2-inch radius then your rifle would still be at 1 MOA. Hitting a 10-inch group at a distance of 500 yards can be calculated as 2 MOA.
There are two more numbers that are important in shooting. The Milliradian or MRAD determines the angle bullets need to travel to hit a given target. When bullets are shot over a long-range, they travel in an arc rather than a straight line. The farther they go before hitting the target, the bigger the circular arc that they travel.
This circular arc that the bullets travel is measured in MRAD. Without going into any complicated math, we can calculate 1 MOA as roughly equal to a 3.6” inch at 100 yards.
Last but not least is eye relief. The eye relief shows how far away your eye needs to be to the eyepiece so that you get the full field of view. A scope with higher power will require you to get close to the eyepiece while a lower-powered scope generally has a greater eye relief distance.
In this post, we reviewed some of the important numbers and readings on the rifle’s scope. A better understanding of these numbers leads to better aiming and accuracy for shooters. Do you have more questions or something to add? Please leave a comment below!