How to Choose a Rifle Scope

Larry Potterfield • January 17, 2023

Choosing the right scope for your rifle is a straightforward process. Let me show you how it's done.

One of the reasons shooters choose to mount a scope on their gun is because it's faster and easier to look through a scope at the target than to have to line up the front and rear sights on the target. Another reason is that the scope generally magnifies the target making it easier to shoot accurately.

Let's begin by taking a look at some scope terminology:

Tube: this is the main body of the scope. Most scopes have a 1 inch or 30 millimeter tube, while some inexpensive rimfire scopes have a 3/4 inch tube.

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Objective Bell: this is the end of the scope farthest from the shooters eye and holds the objective lens which controls the amount of light transmitted through the scope. Usually, the higher the power of the scope the larger this lens will be.

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The Eyepiece: this is the metal part that holds the lens closest to your eye, the ocular lens.

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The Power Ring: on variable power scopes, the power ring changes the magnification of the scope and it's marked from the lowest to the highest power.

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The Windage Adjustment Dial: this is sometimes referred to as a turret on hunting scopes. It's usually covered with a cap but may be exposed on target and varmint models. Turning this dial moves the bullet impact left or right.

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The Elevation Adjustment Dial: this is similar to the windage adjustment dial, but turning this dial moves the bullet impact up and down rather than left and right.

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Some scopes have a side focus, some an adjustable objective, and a few have a knob to light up an illuminated reticle.

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Now that we know the basic parts of a scope, let's take a look at how they work together. "Eye relief" is the distance from your eye to the ocular lens when your eye is properly positioned. A longer eye relief can prevent the scope from hitting you in the eyebrow when firing the gun. This can be especially important on larger caliber rifles.

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The field of view is the width of the viewing area in feet when looking through the scope at 100 yards. For scopes of equal power, a larger field of view is a plus.

Ever wonder why some scopes have a larger objective lens? A scope doesn't gather light, it transmits light. A larger objective lens allows more light to transmit through the scope. The "exit pupil" is a calculation which tells how much light is being transmitted through a scope. It's simply the objective lens in millimeters divided by the power of the scope. In the case of a 4.5x - 14x scope with a 50 millimeter objective, the exit pupil is 11.1 millimeters when the scope is set to 4.5x and about 3.6 millimeters when set at 14x. A larger exit pupil means more light is being transmitted through the scope, which makes it less critical that your eye is perfectly centered in the scope. That's why at dusk it's easier to see on low power than high power.

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Any scope power higher than one magnifies the target. Fixed power scopes are available in a number of magnifications. In this case, "10x" means the target is magnified 10 times with the 40 millimeter objective lens.

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Variable power scopes are generally identified with a set of numbers like 6-18x 40mm. This scope has a range of magnification from six power to eighteen power with the forty-millimeter objective lens.

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Having a variable power scope allows you to turn down the power for closed shots or turn it up for longer ones, which brings up the next point; what power scope do I need?

Well, it all depends on what you're using it for. On my safari rifle, I like a low-power variable scope like this Leupold 1.5-6x. I can dial down the power for close shots at dangerous game or dial it up to 6x for longer shots at plains game.

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One of my varmint scopes is a 6.5-20x with side focus. Most shots are at longer ranges, and the higher magnification lets me clearly hold on the smaller targets for increased accuracy.

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The most popular scopes are what I call the mid-range variables like the one on my 300 Winchester Magnum. In this case, I've chosen a 3.5-10x. This is what I prefer for general big game hunting like deer and elk.

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Long-range precision shooters may choose a tactical scope because of the outside adjustable turrets, side focus, and a large objective. Or they may choose a fixed-power scope with an adjustable objective like a 36x designed for target and bench rest shooting.

One of the biggest decisions is which reticle to choose. The reticle was originally called a "crosshair" because it was made by crossing two fine wires almost as thin a hair, like on this vintage Winchester A5 made in the 1920s.

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The most popular reticle today is the duplex. I like a dot reticle in my varmint scope. There are many more reticles to choose from--even illuminated and bullet drop-compensating versions. It really comes down to your personal preference for the intended use. Many scopes are available with a choice of reticles.

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Scopes are also subject to parallax error. If you've been at the range with a good solid rest and seen the crosshairs move on the target with the slight movement of your eye, then you know what parallax error is. Some scopes have an adjustment to eliminate parallax error which keeps the reticle from moving in a relation to the target.

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The standard location for a reticle is in the second focal plane (cylinder between the adjustment dials and the eyepiece). This keeps the reticle at a constant size, regardless of the power setting on the scope. If you're considering a long-range tactical scope you may want a reticle in the first focal plane (the cylinder between the adjustment dials and the objective bell). When the reticle is in the first focal plane, it appears to change size but always covers the same amount of the target regardless of the power setting since the reticle is a constant size relative to the target. A scope with the first focal plane reticle can easily be used for range estimation.

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Another feature to consider is the type of windage and elevation adjustments. MOA, or Minute of Angle, is a unit of measure which equals 1.0472 inches at 100 yards, but it's usually rounded to one inch. Most hunting scopes have one quarter MOA adjustments which will move the bullet impact approximately one quarter inch per click, or graduation, at 100 yards. At 50 yards the movement is half as much, or one eighth inch per click, and at 200 yards it's twice as much or one-half inch per click.

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Some tactical and long-range scopes use "mil," or milliradian, adjustments rather than inch adjustments. A mil is defined as 1/1000 the distance to the target, regardless of whether the distance to the target is measured in yards or meters. At 100 yards, 1 mil equals 3.6 inches and at 1,000 yards one mil equals one yard.

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A scope with a first focal plane mil-dot reticle and mil adjustments makes ranging a target faster and easier and may be the ultimate long-range tactical scope and, as you might guess, they're pretty expensive.

--Larry Potterfield