Complete Guide to AR-15 Red Dot Sights

Types of Red Dot Sights

Red dot sights are a general term to describe any type of optic that uses a dot (typically from a red LED) to establish an aiming point. Of course, the color can vary as well as the aimpoint symbol (reticle), so instead of a red dot, it can be a green dot or even a crosshair to provide an aimpoint for the shooter.

In simple terms there three major categories of Red Dot Sights:

1. Reflex Sights

Reflex sights are the most common and least expensive category of red dot sights. They are called reflex sights since they use a reflection of a dot or some type of aimpoint on a lens that the shooter looks through to aim. They are typically non-magnified and will either be exposed, also known as windows (single lens), or inside a tubular housing (typically multiple lenses).

Exposed Reflex Sights

The square, exposed red dot sights (like the Burris Fast Fire above) offer a wider field of view for most shooters. Using the two eye aiming method, there is simply less to interfere with your vision. These open sights are often less bulk and often lighter.

Tube-Style Reflex Sights

The benefits of the tube-style (like the Vortex Sparc 2 above) is a more durable, and protected optic. Tube sights are often capable of suffering more abuse than an open sight and are often more waterproof. The tube design, for the most part, is not heavy, but tube styles are often heavier than comparable open sights.

Both the exposed and tube style reflex sight generally use batteries to provide the dot, although sometimes the tube style reflex may use tritium, a beta-emitting radioactive isotope of hydrogen that emits light. Don’t worry, it’s safe!

Reflex Sight Pros and Cons

Unlimited Eye Relief

Unlike other sights, non-magnified reflex red dots have unlimited eye relief. This means there is no set distance you need to have your eye from the sight. Other types of optics require your eye to be a set distance whenever you intend to use it.

Parallax Free

Reflex red dots are nearly parallax free, this means when you move your head around, the red dot moves with you so you’re still pointed at the same spot. This is really nice and allows you to keep both eyes open while using the weapon making it easier to acquire your target. This is unlike other optics that require your face to be a specific distance from the optics every time you shoot to have accurate results.

Cost

Reflex sights are generally less expensive than other types of red do sights. Like most things, depending on your budget you pay a lot or a little. See my recommendations at the bottom based on your budget.

Magnification

Reflex sights are typically non-magnified making them better suited for close range shooting, often 100 yards or less.

However, you can try to have the best of both worlds by using a flip-to-side magnifier that goes behind your red dot. This allows you to quickly flip up the magnifier when you want to take a long-range shot and then flip it out of the way for close range shots.

Vortex Optics VMX-3T Magnifier

Another option is to mount a red dot reflex sight on top of your scope allowing you to switch between the two depending on the distance of your shot.

2. Prism Sights

Prism sights (like this Vortex Spitfire 3x) are typically a short tube style optic with low levels of magnification making them better for longer range shooting compared to non-magnified reflex sights.

Rather than using a series of lenses like a traditional rifle scope, a prism sight uses a prism to focus the image you see down the sight making them smaller than the traditional rifle scope. Prism sights are ideal for the average target shooter or distance shooter.

Prism Sights Pros and Cons

Magnification

As stated, one of the nice features of prism scopes is that they are typically magnified making it easier to hit your target further down range. They are also available with illuminated or etched reticles adding to the experience of shooting your AR.

Short Eye Relief

The biggest issue with prism sights is that they have shorter eye-relief, which means that your eye has to be closer to the optic to have a proper sight picture, just like a traditional rifle scope. This short eye-relief can make it difficult to reacquire your target.

Cost

Prism sights are somewhat more expensive than reflex sights, however, the prices are consistently dropping as time goes on making them an affordable option.

3. Holographic Sights

Holographic sights (like this EOTech 512.A65) are not as common as reflex sights or prism sights typically due to the higher price tag. They are similar to exposed reflex sights in what they offer for field of view and target acquisition only better in quality.

A holographic sight uses a picture of a reticle that is in between glass layers that allows the shooter to look through a glass window and see a holographic reticle superimposed at a distance. The hologram of the reticle is built into the window and is illuminated by a laser.

This is similar to the technology that fighter pilots use for target acquisition. It creates an accurate image of a target even in poor-visibility conditions like rain, snow, darkness or cloud cover.

Holographic Sights Pros and Cons

Peripheral Vision and Target Acquisition

One of the biggest benefits of this type of sight is the ability to maintain your peripheral vision while shooting, because of this you ideally want to mount an EOTech toward the front of your receiver. Mounting it to close to the back of the receiver will prohibit you from having this large advantage.

The heads-up display of a holographic sight allows the shooter to keep both eyes open while shooting. This eliminates blind spots and tunnel vision.

Accuracy & Quality

There’s a reason that EOTech holographic sights are so popular with the United States military. EOTech sights are very precise and will allow for more accurate shooting over long distance. Typically the reticle dots in EOTech sights are 1MOA which means that at 200 yards the dot is going to take up 2 inches on the actual target.

 Cost

Most holographic sights will be several times more expensive than a good quality reflex sight, although the prices have dropped a lot over the years.  In the end, you’re paying for reliability, a clearer dot, better weather resistance, and better shock resistance.

Important Considerations When Buying A Red Dot Sight

Recoil and Caliber Specific Optics

Even though red dot optics are actually simple devices, it is still important to consider what weapon and what caliber that weapon is when selecting your optics. Some red dots feature marked reticles for specific calibers which means if you are running an AR-15 in 458 SOCOM, know that a sight with reticle marks for rifles running 5.56 will not be accurate.

A problem that may be encountered with small budget red dots is recoil. If you are using a weapon that has more recoil than the optic is rated for you may have problems with the sight holding your zero. There are many cheap red dots available under a $100 that have mixed reviews. You may get lucky with one of these or maybe you won’t. I prefer to buy once and cry once.

Battery Life

Battery considerations come down to two main issues. types of battery, and battery life. With some many red dots available, and made by different manufacturers, those batteries vary wildly between companies. As a shooter, you should examine any other electronics mounted to your rifle and attempt to consolidate to a single battery source.

Another issue is battery availability, some sights use weird and difficult to acquire batteries.

Reticle Size

Most red dots are measured in MOA, or minute angle. A 1 MOA red dot is 1 inch in diameter when aiming at something 100 yards away, 2 inches at 200 yards, 3 inches at 300 yards, and so on and so forth. Red dots are available with 1 MOA dots like on the center of an EOTech or much, much larger.

It makes sense that a smaller reticle is better for placing precise shots at longer distances. The dot will cover less of your target making it much easier to pick your aimpoint. The downside is that a small dot is less ‘eye-catching’, and more difficult to see. This is especially true in areas with extremely bright daylight although many higher quality models allow you to adjust the brightness.

Red Dot Sights and Astigmatism

Maybe you purchased your first red dot sight and notice your dot is blurry or star-shaped. You may have an inexpensive or defective optic, however most cases this occurs due to the shooter having an astigmatism.

If you have an astigmatism there are a few things to try to improve the blurry dot you are seeing.

An astigmatism causes light to refract to multiple focal points in your eye, so it is possible to reduce blurriness or irregularly shaped dot by reducing the amount of light going into your eye from the red dot.

Here are some options that may consider:

• Reduce the brightness setting on your red dot
• Focus on the point of impact on your target rather than the red dot
• Use the peep on your backup iron site and red dot at the same time
• Wear polarized sunglasses

If none of these options improve your dot shape and blurriness, you may want to consider a prism or holographic sight mentioned above since many shooters with astigmatisms report better results than with using reflex sights.

Price

Everyone comes to the market with a different budget. What you desire in your sight and how much you can afford will largely determine which optic you go with. Below are several great starting points based on different price ranges, check the reviews for yourself.

Best Budget Red Dot Under $100: Bushnell TRS-25

Best Red Dot Under $200: Vortex Optics Sparc AR Red Dot

 Best Red Dot Under $300: Vortex Sparc AR 2 *Editors Pick*

Best Red Dot Under $400: EOTECH 512.A65 Tactical HOLOgraphic

Best Red Dot Under $500: Aimpoint PRO

 Why Use a Red Dot Sight Over a Scope?

All weapons should be looked at as tools for specific jobs which means you need to have a goal or purpose when outfitting your AR. If you are looking to ring steel targets at 1000 yards, a red dot sight is not the tool you want or need.

Most red dots are 1x magnification making them ideal for shorter distances, although this mainly depends on the shooter. One of the main reasons you would select a red dot sight for your AR-15 is speed and quick target acquisition. If you want to pop off a lot of rounds quickly and accurately, a red dot sight is a way to go.

Lastly, a red dot sight will typically weigh less than a scope and will be far easier to acquire your target without dealing with eye relief.