Rifle Scopes Buyer's Guide

Choosing the right rifle scope will help you shoot with much greater speed and accuracy compared to struggling with the wrong scope or using iron sights.

With hundreds of rifle scopes available to choose from in a staggering variety of types, sizes, and prices, figuring out which scope is perfect for your rifle can be an intimidating process. We are going to tackle rifle scopes by type, giving you the concept behind each category and the pros and cons involved.

Then we’ll talk about types of reticles, the different features you’ll find on rifle scopes, and a few specifications that are important to understand. The right solution won’t just interface well with your rifle, it will interface well with you and the kind of shooting you intend to do.

Prism Scopes

These scopes achieve a fixed magnification in a relatively small package by re-directing light through an internal prism instead of passing it through a series of lenses lined up in a row.

You may read terms like “Pechan prism”, “Porro prism” or “Roof prism” when researching these scopes, but the bottom line is that this technology was originally developed for binoculars and is extremely well-proven.

Rifle Scope

PRO: Prism scopes make a great choice for a basic, super-tough “do it all” scope. Simple to set up, simple to operate, they are less heavy and bulky than conventional rifle scopes with similar magnification levels and features.

Due to their unusual shape, prism scopes usually come with a mounting system already installed. The superb performance delivered by thousands of Trijicon ACOG prism scopes in military service gives this design an enviable reputation for durability in harsh conditions.

CON: Prism scopes are always a fixed magnification, so they don’t have the flexibility of scopes that can “zoom” in and out. Some models can be difficult to mount on some types of rifles due to the inability to interface with specialized mounting systems.

unless the prism scope features a modular mounting system, you’ll have to make do with the mount that is permanently attached. Some models, like the famous ACOG, are so simple that they don’t feature an adjustable ocular ring—if the reticle is not sharply in focus for your eyes, there’s nothing to do but choose a different optic.

You can learn a whole lot more about the Primary Arms line of Gen II Prism Scopes by clicking here.

ar scopes

Low Power Variable Scopes

These generally feature 1x or 1.5x as of the low end of their magnification range, and 4x, 6x, or 8x as their highest magnification setting. Offering maximum flexibility, these rifle scopes promise a both-eyes-open “red dot” type of sight picture that is very fast at close range, plus the ability to increase magnification for confident target identification and accurate shooting out to the medium range.

If you’re looking for good speed and reasonable accuracy at target distances from 10 ft to 600 yards, the low power variable optic (LPVO) is tough to beat.

PRO: LPVOs are the most flexible scopes when it comes to getting on target fast at a wide variety of ranges. At 1x they are faster to use than 2.5x-5x fixed magnification prism scopes at close range. Yet they often feature more total magnification than prism scopes for easier use at medium range.

Using standardized tube sizes gives you the ability to pair up your favorite LPVO with the mount that is also optimized for the type of rifle you have and the type of shooting you do.

CON: You pay a penalty for all this flexibility. Compared to a red dot or prism scope, choosing the LVPO will often double the length and weight of the scope sitting atop your rifle. There is also a hidden cost involved, because you absolutely need a quality 1-piece mount or a set of rings to attach the LVPO to your rifle, which you will have to buy separately.

You can read more about the battle for supremacy between prism scopes and LPVOs in this Scope University article.

Medium Power Optics

These include magnification ranges traditionally used for hunting applications, although their use is not exclusive to hunters. Traditionally, the most popular medium power magnification range was 3-9x, although that has been stretched to 2.5-10x with modern technology.

These rifle scopes trade some speed up close for even more magnification and clarity at longer distances. If shooting fast with both eyes open at ranges closer than 50 yards is not your goal, there is little harm in moving the magnification range up a notch.

ar 15 scope

PRO: Longer effective range with greater accuracy made possible by increased magnification on the top end. A great choice for hunters and other shooters who like a lot of magnification to “zoom in” and take careful, precise shots from 100 yards and beyond.

CON: Medium range scopes can add even more bulk and weight than LPVOs. It will take much more practice to shoot comfortably with both eyes open, and the sight picture will not be as fast to acquire at low magnification, slowing you down at a short-range.

Precision Rifle Scopes

These scopes usually feature maximum magnification ranging from 14x all the way up to 30x. These rifle scopes add cost, weight, and bulk as magnification increases.

The largest, most powerful precision rifle scopes will make your rifle entirely impractical to shoot standing up at the close range. They are only intended for supported shooting from a bench or from the prone position at medium to long range targets. However, if you really want consistent accuracy at serious distances, there is no substitute for a high magnification precision scope.

rifle scope

PRO: See and hit targets from very, very far away. At closer ranges, maximize accuracy with a crystal-clear sight picture and enough magnification to make the target seem just a few steps away.

CON: The biggest and heaviest of all rifle optics. The size and weight of these rifle scopes combined with the need for repeatable precision demands a stout, heavy and expensive mounting system be used as well. Very slow to use, if not impossible to use quickly at close quarters ranges. Prices generally start higher than the other rifle scope options and climb even higher from there. Precision costs money —how precise do you want to get?


Reticle refers to the sight picture or aiming point(s) you see when looking through the scope. The oldest reticles were simple crosshairs made of wire or even silk thread physically strung across the scope tube. Almost all modern rifle scopes now use chemical or laser etching, which can reproduce complex shapes with tremendous consistency. A huge variety of reticle types are now available. The reticle you choose should depend on your performance expectations and what kind of shooting you intend to do with your rifle.

ar15 scope

Traditional duplex crosshairs are thin in the center and thicker towards the edges. Mil-dot reticles utilize methods of target range estimation and bullet drop compensation adopted by the US military about 40 years ago. Long range precision scopes often feature grid reticles, an expansion of the mil-dot concept with standardized holdover points to help the shooter account for wind as well as bullet drop at any target distance. Bullet drop compensation reticles are pre-calibrated to match certain calibers fired at certain velocities, giving simplified aiming cues that approximate the bullet’s impact at increasing distances.

Primary Arms champions the Advanced Combined Sighting System (ACSS), a state-of-the-art reticle concept combining range estimation, moving target leads, bullet drop compensation, and wind holds into the scope’s sight picture.

Reticle illumination uses a battery-powered LED emitter or fiber-optic tube to shine a light on the etched reticle, which has been treated with a reflective coating. The light scatters back towards the shooter’s eye, changing the color and brightness of the reticle.

Reticle illumination helps create a stronger contrast between the reticle and the target for improved speed and accuracy, especially in low light conditions like dawn or dusk. Red and green are the most popular reticle illumination colors. In partially illuminated reticles, only a specific section of reticle has been treated to reflect light, usually to give the user a simplified, faster sight picture when shooting in challenging lighting conditions.

ar15 scope


These refer to mathematical angular units of measure. The Minute Of Angle (MOA) system is traditional in the United States, with 1 MOA covering a circle measuring 1.047 inches at 100 yards.

The Miliradian (MRAD or MIL) system is easy to work with for shooters familiar with the metric system, with 1 MIL covering 10 centimeters at 100 meters. Regardless of which system you choose, for long-range precision shooting applications it is important for the calibration of windage and elevation adjustments to match the mathematic system used in the reticle. Scopes with MOA reticles often feature 0.5 or 0.25 MOA-per-click adjustments, while scopes with MIL reticles often feature 0.1 MIL-per-click adjustments. For lower magnification scopes featuring BDC reticles and other “set it and forget it” designs where turret clicks aren’t cross-referenced with the reticle to compensate for bullet drop at various ranges, it is less important for the “turret math” to match the “reticle math.”

ar15 scope

You can get a much better understanding of MOA and MRAD in our sight-in article, How to Zero Like a Hero.

Sedcond Focal Plane (SFP)

These optics feature a reticle that stays the same size relative to the field of view at all magnification settings. Whether at minimum or maximum magnification, the sight picture will always stay constant.

The advantage of SFP scopes is that they are usually less expensive than similar first focal plane optics. The disadvantage of SFP scopes is that advanced reticle features like bullet drop compensation can only be “true” and correct at one magnification setting, usually maximum magnification.

First Focal Plane (FFP)

These optics feature a reticle that stays the same relative to the target, not to the field of view. As you “zoom” from minimum to maximum magnification, the reticle will appear to grow as the target becomes larger inside the field of view. The advantage of FFP scopes is that the reticle’s advanced features are always “true” regardless of the magnification setting. The main disadvantage of FFP scopes is that they usually cost more than their SFP equivalents.

Low magnification scopes are more likely to use the SFP configuration, while high magnification hunting or precision optics are more likely to use the FFP configuration. You can dive deeper into understanding FFP and SFP by checking out this Scope University article .

Adjustment Knobs

These control the position of the reticle relative to the target being viewed through the scope. Initially, the turrets are adjusted to sight-in or “zero” the rifle so that point of aim coincides with the bullet’s point of impact at a specified distance.

When shooting at a variety of distances, the elevation turret may be used to compensate for bullet drop, and the windage turret used to compensate for the effect wind has on bullet trajectory.

rifle scope

scope turrets

Zero-resettable turrets can be positioned to read “0” after initial zeroing, making subsequent adjustments for range and wind much easier to work with, and providing an easy reference to check that the turrets have not been accidentally turned or bumped out of their intended position.

Locking turrets can be locked into a position the user determines, helping prevent accidental scope adjustment during rough handling. Finally, some scopes intended for long-distance precision shooting feature a “zero stop” elevation turret. Zero stop turrets allow the user to mechanically set a point where the turret’s rotation will physically stop.

In case the optic needs to be returned to its original zero quickly after being adjusted for a long-range shot, the turret can be spun back down to the rifle’s original “zero” without the need to carefully count clicks or observe the turret’s markings.

Adjustable Ocular Lense

Sometimes called diopter rings or fast focus eyepieces, adjust the focus of the reticle as viewed through the scope.

ar15 scope

They do not affect the focus of objects viewed through the scope. The diopter only needs to be set once to use the reticle at any distance, but the perfect diopter setting varies from person to person since every shooter’s vision is slightly different.

Parallax Distortion

ar 15 scope

Parallax error occurs when the target’s image and the reticle are not aligned on the same focal plane inside the scope. Eliminating parallax error brings the reticle into the same focal plane as the target, maximizing accuracy and consistency.

While eliminating parallax error also generally brings the target into sharp focus, parallax and focus are not the same things. Parallax error is most noticeable at high magnifications and most important in precision shooting.

Lower magnification scopes like prisms and LPVOs are generally set to eliminate parallax error at 100 yards only, with no adjustment feature.

What is Tube Size?

Tube size refers to the diameter of the main body of the scope tube. The most common tube sizes are 1-inch and 30mm, but 34mm and 35mm scope tubes are often used in premium optics. When choosing a mount or rings for your scope it is crucial to match dimensions with the scope tube size.

what is Field of View?

This refers to the distance between the edges of the scope’s sight picture at a certain magnification. The field of view is usually expressed in feet, at 100 yards, at a specific magnification.

For example, the Primary Arms 1-6x Gen III scopes have field of view listed as “110 feet @100 yards at 1x” and “19.3 feet @100 yards at 6x”. Imagine standing at one end of a football field and having a friend stretch a tape measure across the end zone 100 yards away.

Looking through the scope at 1x, you would be able to see 110ft of tape measure from one edge of your sight picture to the other. Cranking up magnification to 6x, you would be able to see 19.3ft of tape measure from edge to edge.

Although field of view generally varies with magnification, not all rifle scopes feature the same field of view at the same magnification. All else being equal, maximizing field of view is desirable.

What is eye relief?

Eye relief is the ideal distance between the ocular lens at the rear of the scope and the shooter’s eye. Eye relief can be expressed as a range, for example 3.3-3.5 inches.

This either indicates that the ideal sight picture can be obtained anywhere between the two measurements, or that the ideal measurement changes slightly as magnification increases. Rifle scopes with a shorter eye relief tend to feature more field of view.

Scopes with a longer eye relief can be mounted on high recoiling firearms without risk to the shooter’s eye as the optic violently moves rearward with each shot.

What is exit pupil

Exit Pupil is the diameter of the shaft of light coming out of the ocular lens located at the back of the scope. To look through the scope, the pupil in your eye needs to look down that shaft of light.

Exit pupil is a function of objective lens diameter divided by magnification, so the same scope can have a generous exit pupil at low magnification and a much smaller exit pupil at high magnification. The human eye can only open to a maximum diameter of around 7mm, so old conventional wisdom held that exit pupil specifications larger than 7mm were wasteful, since the scope is delivering more light than your eye can accept anyway.

In recent years, however, the close relationship of exit pupil to “eye box” has become understood. Eye box cannot be quantified with numbers, but describes an imaginary box drawn at the scope’s eye relief.

Placing your eye anywhere inside the eye box will result in a useable sight picture through the scope. A wider exit pupil helps create a large, “forgiving” eye box beneficial to rapid sight acquisition, creating a better opportunity to find the reticle through the optic and take an accurate shot even if the eye is not perfectly aligned with the scope’s centerline.

If you are researching which rifle scope is best for your AR, AK, or precision rifle and you have a technical question, feel free to call 713-344-9600 or email info@primaryarms.com. Our dedicated customer service team here in Houston, Texas is standing by to help!

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