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Rifle manufacturers are consistently making improvements to their scopes to offer hunters and rifle enthusiasts reliable equipment. With a wealth of models on the market, it can be difficult to decipher the evolving technology and how best to capitalize on the functions to improve your shooting experience. You may be an experienced shooter and still ask “what do the numbers mean on a rifle scope?” So do not worry, we have gathered everything you need to know!
What Do the Numbers Mean on a Rifle Scope?
The numbers on a rifle scope reflect the range of its magnification (or power) and the size of the objective lens. The first 2 numbers relate to the minimum and maximum magnification level of the scope, also known as the zoom scope, whilst the last number refers to the objective lens diameter in mm. Navigating and understanding these numbers are critical for improving the speed and accuracy of your shot.
Magnification or Power
A rifle scope’s primary function is to magnify the chosen target, and the most common series of numbers you will see on a scope signify the magnification level.The magnification, or power, is specified as a multiplication factor compared to the naked eye, meaning that a target in the reticle of a scope with a ‘3-9′ power range can appear 3 to 9 times larger depending on where the shooter sets the zoom.
The first number signifies the lowest magnification and the second number the highest. Some scopes with a fixed power will just have one number; for example, ‘4x40mm’. This signifies that the target in the reticle of this scope will appear four times larger, or four times closer, than the naked eye. The higher the number, the higher the magnification.
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Variable power on a scope will always have the numbers separated with a dash, and most modern rifle scopes will have this capability. Variable power enables a shooter to have far greater versatility at the range or in the field because of the number of values that can be set in between the lowest and highest settings.
Deciding on the power of your scope will depend on the environment and the expected distances to your targets. For example, if you are hunting in thick forest or areas of close cover, you would be better off using a low-power fixed scope, like a ‘4x’ or a variable power scope with a low power of 3.5x or lower. This increases your overall field of vision, which can allow you to quickly acquire the target and freely switch to other targets.
If you are operating in mountainous areas or long range environments, then a rifle scope with a high fixed or variable power is the best option (i.e: ‘16x’ or a ‘20x’). This will provide the shooter with a clear image of a small target even if it’s hundreds of yards away. Most hunters will opt for rifle scopes with variable powers like ‘3.5-10x’ or ‘4-12x’ because they allow for large variations from long range to close cover.
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Objective Lens Size
This is the final number in the sequence and signifies the objective lens size in millimeters (mm), also referred to as the objective diameter of the scope. For example, the ‘3-9×40′ scope has a variable power of 3 to 9 times and an objective diameter of 40mm.
The objective lens of a scope is the one closest to the target and farthest from the rifle’s stock. The larger the lens, the greater its capacity to let light in, and as a result the target will be illuminated. The more a scope magnifies a target, the larger its objective diameter needs to be to maintain brightness and clarity. For instance, a ‘3-9x32mm’ scope will not be as clear on 9 times magnification than a ‘3-9x50mm’ scope, which will be bright on all variable power settings.
Rifle scopes with low objective diameters will get darker and darker the more you magnify the target, so opting for a larger objective lens will be of great benefit, especially in low-light conditions.
In low-light conditions, scopes with larger objective diameters are more effective due to their larger exit pupil. The exit pupil is the size of the beam of light that leaves the scope and can be calculated by dividing the objective diameter by the power. For example, a ‘4x32mm’ scope will have an exit pupil of 8mm. To help put this in perspective, the human pupil on a clear sunny day will vary between 2mm to 4mm depending on the brightness. At pre-dawn or after sunset, the pupil will vary from 5mm to sometimes as high as 9mm.
So, even though a scope with a larger exit pupil will have a minimal effect during the day, it will be a huge benefit to precise vision in low-light conditions.
Tube Diameter
Tube diameter is the diameter of the scope’s tube. When you’re wondering “what does the numbers mean on a rifle scope,” you should know that you aren’t likely to find this number displayed on many scopes; but it is found on the manufacturer’s box in the description and details. You will need to know this number as it’s necessary for purchasing the correct rings to mount the scope on your rifle.
Two of the most common sizes for scope tubes are ‘1inch’ and ‘30mm’, with the latter being the largest. A larger tube diameter enables the lenses inside the scope to be larger, allowing more light to pass through for clearer vision. ‘30mm’ tube diameters are often more expensive, with ‘34mm’ versions being even more so.
How the Scope Works
A fundamental part of answering “what do the numbers mean on a rifle scope?” is understanding the basic workings of the scope. The scope has four main components: the glass, optical coatings, parallax adjustment and eye relief.
Glass (the Lens)
High-definition glass or extra-low-dispersion glass (ED glass) is used to make the lens of the scope. It directs the wavelengths of external light into a focal point, increasing clarity, sharpness and true-to-life colors.
Optical Coatings
Reflected light in rifle scopes is the main cause of decreased light transmission and blurry images. When light hits a glass surface, between 1% and 5% of the light is reflected. To eliminate this chance of reflection on the ED glass, manufacturers coat the surface with a thin chemical film (commonly magnesium fluoride). Multiple layers reduce glare and light loss, which results in vibrant, clearer images.
There are three main terms used to describe the types of coatings available for your optics:
- Coated – Single layer on the exterior surfaces of the glass for protection from abrasion
- Multi-coated – Multiple coats on the exterior surfaces of the glass to prevent abrasion and reduce glare
- Fully Multi-coated – All glass surfaces are thoroughly coated to maximize durability and the best light transmission
Parallax Adjustment
Every scope has a standard focusing knob which adjusts the reticle to your eye. The reticle is the series of fine lines in the eyepiece that measures the scale/size of distant objects. Parallax occurs when you are viewing distant targets, with magnification over 10x, and the reticle appears to shift or move. To return the reticle to the same focal plane as the target, use the parallax adjustment.
Most scopes that do not have adjustable objectives compensate for parallax by being preset to find focus at 150 yds. However, if you are looking for a higher power scope for distant targets, consider one with an adjustable objective.
Eye Relief
Eye relief refers to the physical distance that you can hold the scope from your eye without losing sight of the entire image The eye relief on a rifle will vary with the power of the scope, but try to find options with generous eye relief, as it will allow you to acquire the target more quickly, especially for running shots.Most hunters will use 3″ to 4″, but for those of you with large magnum rifles, you will need maximum relief to avoid injuring yourself when the rifle recoils.
Common Terms to Understand
If you are new to rifle scopes, you will probably encounter terms you don’t understand. To avoid confusion, we have defined a few important terms that will help answer your question “what do the numbers mean on a rifle scope?”
Field of View (FOV)
The field of view references how wide the area is (in feet) that you can see at 100 yds. The higher a number is, the wider the area appears, while a smaller number indicates a narrower area. Therefore, as you increase the magnification, the FOV becomes smaller. These numbers are influenced by the focal length of the objective lenses, the design of the eyepiece and the power of the scope. If you are interested in close cover, quick-target acquisition, you will need a wider field of view, so you should seek a smaller power.
Minute of Angle (MOA)
When designating variances on a target at 100 yds, MOA is the term used to describe the adjustment on a scope. To calculate MOA at any distance, just multiply the distance in yards by 1.047 and then divide by 100.
For example: If the adjustments on the scope are 1/4 MOA, then the bullet’s point of impact will move 0.26175″ (rounded to 1/4″ at 100 yds) for every click of the adjustment knob.
Milliradians (MILs)
MILs serve the same function as MOA. They are both equal at 100 yards, but their math is different:
- 1 MOA = 1.047 inches or 1/4″ at 100 yards
- 1 MIL is equivalent to 3.438 MOA
- To calculate the inches in 1 MIL, multiply 1 MOA (1.047″) by the amount of MOA in 1 MIL (3.438)
Conclusion
Understanding these terms, along with the components of the scope and its numbers, will ultimately improve your overall accuracy, speed and target success when shooting. We hope this has helped to answer “what do the numbers mean on a rifle scope?” If you are seeking a way to improve your confidence and success rate when shooting, take time to familiarise yourself with your scope and then practice with a target!