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12 Things You Need to Know About Rifle Optics

Some basic information is essential to selecting the right optical sight for your operations.

January 28, 2016  |  by - Also by this author

The Trijicon ACOG is kind of a hybrid optic, offering magnification and speedy CQB target acquisition.
The Trijicon ACOG is kind of a hybrid optic, offering magnification and speedy CQB target acquisition.

Now that many law enforcement agencies allow their officers to field rifles, rifle optics have become very common in law enforcement operations.

In order to help you decide what optic best suits your needs, POLICE Magazine spoke with some experts on the tactical operation of firearms optics. And the following are 12 things they said you need to know about these essential accessories.

1 Types of Optics

There are two categories of firearms optics: telescopic sights and reflector (reflex) sights.

Telescopic sights, commonly known as "scopes," are sights that use magnification to make targets appear closer to the shooter, thereby making it easier for the shooter to make a precision shot.

Reflector sights or "reflex" sights are optics that do not magnify the image of the target and feature a single point of reference such as a red dot for extremely fast sight acquisition. They are very useful in close-quarter combat, especially against multiple targets and moving targets. They can also be used at ranges beyond 200 yards by skilled shooters. One shooter who assisted with this article said he can hit a 12-inch plate about 75% of the time at 300 yards with a short-barreled 5.56mm rifle and an Aimpoint T1 with 3x magnification.

The term "reflex" sight is a shortening of the word reflector. Almost all reflex sights use a mirror and an internal light source such as an LED to reflect the image of the reticle back to the eye of the shooter. However, holographic sights first marketed by EoTech (now L-3 EoTech) use lasers to project a single point of aim onto a film enclosed inside the optic. Although they do not use reflection, holographic sights are generally classified as a type of reflex sight because they offer a single point of reference for quick target acquisition.

2 What the Numbers Mean

Telescopic sights are categorized by their magnification capabilities and tube size expressed as a series of numbers. For example in the product name of the Leupold VX*R Patrol 1.25-4x20mm, the 1.25-4 signifies that the scope offers variable magnification of 1.25 power to 4 power, and the 20mm is the diameter of the objective lens.

Aimpoint's Patrol Rifle Optic (PRO) was designed specifically for law enforcement operations.
Aimpoint's Patrol Rifle Optic (PRO) was designed specifically for law enforcement operations.

3 Optical Terminology

In any discussion of firearms optics, a lot of lingo will get thrown around. Here's a look at a few terms you should know.

Exit Pupil—If you hold a scope at arm's length and point it at a bright surface such as a wall in a well-lit area, you'll see the exit pupil; it's a circle of light. And that circle of light is the amount of illumination that enters the scope. The larger the exit pupil, the brighter the image in the scope will seem.

Eye Relief—This is the distance between the shooter's eye and the eyepiece from where the shooter can see the entire image inside a magnified scope without the dark eclipse effect called "vignetting." Eye relief shifts on a variable power scope as you change the magnification. Tim O'Connor, consumer services manager for Leupold, says shooters need to match the eye relief to their cheek weld. "We get a lot of calls from people who don't have the scope mounted properly for the eye relief. They say something is wrong with the scope, but it's the mounting position not the scope."

Field of View—This is the actual width of what you can see through the scope measured in feet or meters at specific distances. The higher the magnification, the smaller the field of view.

4 Minute of Angle

A minute of angle (MOA) is a unit of measurement that's equal to 1/60th of a degree. One MOA is pretty much 1 inch at 100 yards. In shooting that means all of the shots impact within a 1-inch diameter circle. A 2 MOA sight can help you place all of your shots within a 2-inch circle at 100 yards, a 4-inch circle at 200 yards, and so on.

Leupold's VR*X 1.25-4x20 scope is a variable magnification sight that features the company's Firedot SPR reticle.
Leupold's VR*X 1.25-4x20 scope is a variable magnification sight that features the company's Firedot SPR reticle.

5 Types of Reticles

The reticle is the aiming indicator inside the optic. It can be the center point of an old-fashioned crosshair, a red dot, a ring, a horseshoe, or any number of other shapes.

Reticles on close-quarter-combat (CQB) sights are usually measured in MOA. Scopes used by snipers to make very precise or long distance shots have reticles measured in miliradians (1/1000 of a radian). Trained shooters can use mil-dot reticles and math to calculate the range to targets, the size of targets, bullet drop, and wind drift so they can make shots at substantial distance.

The red dot-style reticle is much more common on CQB optics. The reticle size on Aimpoint red dot sights is commonly 2 MOA or 4 MOA. Larger reticles are better for quick acquisition of the target in a close-quarter situation and they are easier to see with both eyes open. Smaller reticles are better for precision at distance.

Reticles are often illuminated by battery-powered LEDs, fiber optics, or the radioactive decay of tiny amounts of tritium.

6 Sight in Your Optic

Rob Garrett, a firearms instructor, 37-year veteran law enforcement officer, and writer for some of the nation's leading firearms magazines, recommends that officers sight in or "zero" their patrol rifle optics at 50 yards and at 200 yards, as most law enforcement rifle shots even by precision shooters on SWAT teams are taken at less than 100 yards. "With a 50/200-yard zero, point of impact in relation to point of aim is not greater than 8 inches from zero to 300 yards. That keeps your shots well within center mass," he explains.

It's critical that the actual mechanics of zeroing the optic are performed correctly, and officers should make sure they know what they are doing. Instructors of patrol rifle courses say it's not unusual to find officers who are carrying rifles fitted with optics that have not been zeroed or have not been properly zeroed.

Even once the optic has been zeroed at a specific distance, it's important that officers understand how to take shots closer than that zero point. Shots at close range will strike low on the target because of offset, which is the distance the optic sits above the bore of the rifle. Garrett recommends officers go to the range and try to shoot at dime-size targets from a distance of 7 yards to learn the offset of their optics.

Finally, once you have your sights zeroed, stop fiddling with them. And never let another officer borrow your rifle and start turning the knobs on your optics unless you are certain you can sight it back in. Your rifle optic is a life-and-death tool, and it has to be set up correctly.

7 Bullet Drop Compensation

Some optics such as the Trijicon ACOG (Advanced Combat Optical Gunsight) feature a bullet drop compensator (BDC) that helps shooters hit targets at ranges far beyond the zero points of their optics. Although a BDC sounds like a mechanical device, it is actually a series of marks below the point of aim, point of impact position of the reticle that are marked off in distance. By adjusting the position of the reticle down to one of these range-finding marks or "stadia," the shooter elevates the barrel of the rifle to compensate for the effects of gravity upon the projectile at distance. This is a quick way to make long-distance shots, but it's not as precise as working out the math.

Steiner makes a wide variety of scopes and sights for both precision shooting and close-quarter combat.
Steiner makes a wide variety of scopes and sights for both precision shooting and close-quarter combat.

8 Have a Backup

Regardless of the quality of the optic on your patrol rifle, it can malfunction or be damaged or obscured. Which is why your patrol rifle should be equipped with backup iron sights. Some officers use mounting systems that raise their optics high enough above their rifles so that the iron sights are cowitnessed. Others use quick release mounts that allow them to remove the optics in seconds without any tools. Patrol rifle trainers and experts do not recommend that officers mount their iron sights or their optics in a position that requires them to cant the rifle, which is sometimes done by 3-gun competitors.

9 Get the Training

There are two types of training scenarios for officers who carry patrol rifles fitted with optics. If you work for an agency that issues you a rifle and optic and expects you to carry it, then the agency will provide you with training. If you work for a smaller agency that permits you to carry your own personally owned rifle and optic on the job, then you may not have the benefit of agency-provided training.

Fortunately, officers who carry personally owned rifles and optics on duty have some options for quality training. Sheriff agencies may open up their training to officers from smaller police departments in their counties. Sometimes groups of agencies combine their resources and conduct regional training. And at least one state law enforcement academy is currently organizing a program that will be open to all officers in that state.

But even if you have to find your own certified law enforcement training and pay for it out of pocket or through an allowance from your agency, the one option you don't have is to forego training. Veteran officers advise even the best sport rifle shooters to seek out law enforcement-specific training if they are going to carry a rifle on duty.

Once you have had the training, you should work to make sure your skills don't decay. David Matthews, a 37-year veteran of law enforcement and retired SWAT commander who now serves as Steiner's U.S. law enforcement sales manager, says officers who carry patrol rifles should train with them if not weekly, at least once per month.

10 They're Not Magic

There is a tendency among some shooters to believe that tools like laser sights and optics somehow make up for shooter mistakes. Garrett says, "Regardless of what type of optic you use, proper trigger control is still essential. The red dot does not steer the bullet."

11 Match the Optic to Your Mission

There are optics designed for close-quarter combat and optics designed for long-distance precision shooting. So users of rifle optics in law enforcement operations need to understand their mission parameters and choose the right tool for the job.

But be sure you understand the mission in full. For example, many officers believe magnifying optics have no purpose on a patrol rifle. However, Frank Martello, assistant manager of law enforcement programs for Trijicon, likes to remind officers they need to legally justify the shot, not just make the shot. "With 20/20 vision naked eyes at 30 yards, you can say, 'I think he has a gun.' With a 4X ACOG or other magnified optic, you know he has a gun," Martello says.

12 Before You Buy

It's widely known in law enforcement that when agencies are planning to make a large purchase of equipment some companies will loan them equipment to test. What's lesser known is that sometimes companies will do the same for individual officers. Several of the companies contacted for this article say they offer test drives to individual officers, if they meet certain requirements such as making the request on agency letterhead or through official communication endorsed by command. If there's a sight you are thinking of buying, contact the company and see if it can offer you a test and evaluation (T&E).

Another good way to find out more about the optic you think you want to buy is to find other officers who are using it and ask them what they think. The makers of tactical rifle optics say that word of mouth is extremely important and they take great pains to maintain quality of their products and stay in communication with their law enforcement customers about any requested improvements to the products or to customer service. "Cops talk and we understand that," says Steiner's Matthews.

The final advice that all experts POLICE contacted for this article echoed was you should buy a quality optic from a well-known company.

For More Information


ELCAN (Raytheon)

EoTech (L-3)



Nightforce Optics




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Comments (5)

Displaying 1 - 5 of 5

Bob @ 2/7/2016 10:58 AM

"For example in the product name of the Leupold VX*R Patrol 1.25-4x20mm, the 1.25-4 signifies that the scope offers variable magnification of 1.25 power to 4 power, and the 20mm is the diameter of the tube."

Ah, almost. 20mm is the diameter of the objective lens. That is the one at the front of the scope.

The tube on my 1.5-6x50 is not 50mm. Instead, the objective lens is 50mm. This is important because the larger the objective lens, the more light it takes in. Higher numbers there, work better in lower light situations, all other things being equal.

Bob @ 2/7/2016 11:08 AM

"For example in the product name of the Leupold VX*R Patrol 1.25-4x20mm, the 1.25-4 signifies that the scope offers variable magnification of 1.25 power to 4 power, and the 20mm is the diameter of the tube."

Ah, almost, but night quite.

In this case 20mm is the diameter of the objective or front lens. My 1.5-6 x 50 does not have a 50 mm tube, but rather a 50 mm lens on the front.

This is an important difference for two reasons. First because it allows you to get the proper size scope rings to mount the scope. Second, because the larger the objective lens, the more light the scope takes in. All other things being equal, a larger objective lens will gather more light, making it better in lower light conditions.

Lonegunmann @ 2/26/2016 10:35 AM

Bob, the specific scope they picture is a patrol CQB or scout like scope where the "front bell" is no bigger than the scope body so it is 20mm in that instance. This does limit field of view. What you say is generally the fact however - thanks for the description/detail.

Sarah Smith @ 6/27/2016 9:44 AM

I own a rifle and am hoping to get a nice scope soon so that I can practice with it before hunting season. Thanks for the information about having a backup in case the first scope malfunctions or is damaged. Now I just need to research scopes and find the right fit for my rifle.

John Smith @ 7/18/2017 3:40 AM

Very Impressive article. everyone should need to know the impotent fact before the buying a rifle scope. You wrote the awesome impotent fact in this article.
Thanks for sharing
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