The Ultimate Guide to AR-15 Optics, Sights, Scopes, and More

Building a new AR-15, but you’re not sure what optics you should put on it? Or maybe you’re wondering what exactly the differences between a red dot, prism sight, and holographic sight are? If so, you’ve come to the right place. We’re going to take a look at the different types of AR-15 sights, and go over the pros and cons of each one based on different applications.

Iron Sights

From the classic carry handle rear sights to modern low profile polymer or aluminum flip-ups, the AR-15 platform is certainly no stranger to iron sights. While they may be an afterthought for many shooters in the era of rugged, affordable optics, there is still a strong case to be made for having a solid set of backup irons in case a primary optic breaks, runs out of batteries, or otherwise malfunctions in an emergency situation. If you’re running a magnified optic that simply isn’t designed for close range shooting, a pair of offset iron sights mounted at 45° is another great option, allowing the shooter to quickly cant their rifle to side, fire off shots at a closer target, and then returning to their optic to acquire more distant targets.

If you’re building an AR-15 with home defense or SHTF scenarios in mind, a pair of backup irons is a no-brainer. In exchange for an extra ounce or two of weight and a small bit of rail space, you get a durable, consistent backup option that will ensure you aren’t left shooting blind if you wind up with a drained battery, cracked lens, or loose mounting screw. Just be sure to practice with them once in a while – not only is a good way to drill the fundamentals of marksmanship, it’s also worth getting in the habit of periodically verifying that your sights are still properly zeroed.

Pros:

• Affordable
• Versatile
• Incredibly Durable

Cons:

• Difficult to use at long ranges without practice
• Poor low-light performance
• Slower target acquisition

Red Dot Sight

A red dot sight, or RDS, is technically a type of reflex sight (more on that in a minute), but the typical design is different enough to warrant its own discussion. The idea to attach a reflecting sight to a firearm is older than most people probably think – the first patent for a “collimating-telescope gun-sight” was filed in 1901 by Sir Howard Grubb of the Royal Dublin Society. Because these early designs relied on ambient light or batteries with extremely short lifespans, red dots were regarded as little more than a novelty until 1975, when Aimpoint introduced the first electronic red dot.

Like modern dot sights, Aimpoint’s design used an LED bounced onto a curved and specially coated mirror. By using mercury batteries, this design solved the problem of short battery life, and other manufacturers quickly started producing their own red dots. While the basic technology behind these optics hasn’t changed much since 1975, there have been enormous advances in battery longevity, durability, size, and optical clarity.

Still, it wasn’t until the early 2000s that red dots truly proved their worth in the intense urban CQB environments of Iraq. The military almost immediately saw the benefits of an optic that allowed for lightning-fast target acquisition and the ability to easily track moving targets at typical engagement distances, and as they became common military-issue equipment, the civilian shooting world quickly followed suit, and nowadays you’d be hard-pressed to visit a shooting range without seeing at least one red dot mounted on an AR-15.

Aside from letting the shooter get on target much more quickly, red dot sights offer a number of benefits that make them excellent tools for close-range shooting. An RDS allows you to easily and accurately shoot with both eyes open, maintaining your peripheral vision so that you are able to take in more of your surroundings – an obvious advantage for hunting, combat, or personal defense. They are also virtually parallax-free outside of extremely short distances, which makes it much more likely that your rounds are going to land where you want them to even if the reticle isn’t centered.

They’re also ideal for certain hunting situations – you’ll commonly see them mounted on rifles meant for hog hunting, especially if dense brush or game feeders are involved. If you find that you’re usually taking shots at short distances and against moving targets, a red dot is seriously worth considering as a hunting optic.

Pros:

• Fast target acquisition
• Ability to shoot with both eyes open
• Easy to track moving targets

Cons:

• Can obscure targets at longer ranges
• Budget-friendly options can be not as durable

Reflex Sight

As mentioned earlier, red dots are technically a type of reflex sight, since the term encompasses any optic that uses a projected reticle system. However, there are a few key design differences that make reflex sights worthy of their own discussion.

The most obvious difference is that reflex sights typically use an “open” design which takes advantage of the fact that the sight’s optical window doesn’t need much in the way of a housing. Compared to a red dot sight’s tube design, a reflex sight is a bit more lightweight and gives the shooter a slightly larger field of view, which can be especially useful in close quarters environments. Reflex sights also come in a variety of different reticle options, such as circle and cross reticles, which some shooters find even faster than a dot reticle when it comes to acquiring targets at short distances.

There are a couple of downsides to this design as well, though – the lack of a bulkier housing means that while reflex sights are lighter, they aren’t quite as rugged. It also means that they can’t take advantage of accessories such as anti-haze filters, sun shades, or flip-up covers, which is something to consider if you shoot in unforgiving weather conditions or extremely bright sunlight.

In pretty much every other respect, reflex sights and red dots share the same benefits: unlimited eye relief, lack of parallax distortion, and the ability to shoot with both eyes open using the Bindon Aiming Concept to focus on both the reticle and target at the same time without sacrificing situational awareness.

Pros:

• Wider field of view than most other optics
• Fast target acquisition at close range
• Reticle style and color variety

Cons:

• Higher risk of damage to the lens
• Incompatible with many optic accessories

Prism Sight

Prismatic sights, also known as prism scopes, are a relatively new development in the world of rifle optics, though the basic concept behind their design can be seen used in binoculars and spotting scopes. Unlike the system of image-erecting lenses typically used in telescopic rifle sights, prism sights use (as you probably guessed from the name) roof prisms.

One of the benefits of this design is that the reticle can be etched directly into the surface of the prism, allowing it to remain visible to the shooter even if the active illumination system fails or is turned off. That makes it an attractive option for military, law enforcement, and personal defense applications, which is why you’ve almost certainly heard of the most famous example of a prism sight: the Trijicon ACOG.

In addition to being perhaps the most battle-tested AR-15 sights on the planet, the ACOG is a great example of what prism scopes have to offer – the use of both tritium and fiber optic light pipe provide excellent performance in both broad daylight and low light conditions, the etched reticle provides some built-in redundancy and allows for the addition of bullet drop compensator markings, and the telescopic design means that shooters who are dealing with astigmatism will not encounter the blurriness or double vision that can occur with other types of optics. They are also available in several fixed levels of magnification, ranging from 1x to 6x – but keep in mind that trying to use a magnifier with a prism scope will result in some pretty severe optical distortion, which might make them a less versatile option for some shooters.

Prism sights do have slightly worse eye relief than red dots, reflex sights, or holo sights, but they’re still generous enough that most shooters should have no issues. There’s also the elephant in the room – high-end prism scopes like the ACOG can be eye-wateringly expensive, and if you’re building an AR-15 for anything other than competition use, it’s not unusual to end up with a prism scope that costs more than the rifle it’s mounted on. They’re undeniably great optics, but it’s worth considering if you actually need all of the features that come with that high price tag.

Pros:

• Excellent for shooters with astigmatism or cross-eye dominance
• High-end options are nearly indestructible

Cons:

• Can’t be used with a magnifier
• More expensive that other options

Holographic Sight

While a holographic sight might look similar to a red dot or reflex sight at first glance, a brief look at their internals reveals that they are much more complex. Instead of bouncing an LED off of a single curved lens, holo sights rely on a laser diode, a folding mirror, a collimating reflector, and holographic grating in order to project an image of the target area and reticle.

As you’d probably expect, that added complexity also translates to some extra bulk and a significantly higher cost, and the fact that EOTech and Vortex are the only manufacturers making holographic sights doesn’t help. And while it’s unlikely to be a major factor for most shooters, it’s worth mentioning that the added complexity of a holographic sight also results in a much shorter battery life, with the average holo sight being able to run continuously for 1-2 months compared to the staggering 5 year battery life of some high-end red dots.

Despite a few potential cons, there are plenty of good reasons to consider a holographic sight, too. For one thing, they are incredibly durable – in fact, they can operate just fine even if the optic’s front lens is entirely destroyed! Holographic sights also come in different styles and colors of reticle, and many shooters find that EOTech’s iconic Speed Ring reticle offers an excellent balance between fast close-range target acquisition and longer-range precision. And as with prism scopes, shooters with astigmatism will find a holographic sight much sharper than a red dot or reflex sight.

Pros:

• Excellent balance of short and mid-range performance
• Extremely durable

Cons:

• Shorter battery life
• Bulkier than other close-range optics

LPVO

An LPVO, or low-power variable optic, is intended to bridge the gap between an unmagnifed optic and a traditional rifle scope, especially in tactical situations where target ranges are often constantly and unexpectedly changing. While other optics have tried to account for this problem (such as holographic sights adding compensator markings or telescopic sights with a large ring around the crosshair), they still aren’t an ideal solution to the problem.

LPVOs attempt to address this need for versatility by offering both 1x magnification and the option to quickly increase magnification, often with the use of a throw lever that allows the shooter to rapidly move back and forth through the entire range of magnification while maintaining line of sight on the target. While originally designed for tactical applications, that versatility has also made LPVOs a huge hit in the world of competitive shooting, as well.

As with any optic, there are still compromises to be made: LPVOs aren’t going to outperform a red dot or holo sight at close range, or outperform a dedicated variable-power rifle scope at long ranges, and getting great performance at both ends of the magnification range will cost a pretty penny. But they are a great jack-of-all-trades option if you often find yourself shooting at different distances and don’t want to deal with the hassle of swapping and re-zeroing optics.

Telescopic sights can get pretty heavy, which is why you’ll commonly see them on top of long-barreled AR-15s that aren’t meant to be moved around much, alongside other accessories like fixed stocks, bipods, and cheek risers that all trade weight for improved stability and long-range performance. They’re also a no-brainer on AR-15s chambered for cartridges like 6.5 Grendel, .224 Valkyrie, or 6mm Creedmoor that are capable of reliably putting rounds on target out past 1,000 yards.

Pros:

• Ideal choice for long-range shooting
• Extreme precision

Cons:

• High-power scopes add significant weight
• Requires alternative AR-15 chamberings to maximize potential

Different Applications

Plinking / General Use

If you’re just looking for an affordable all-around optic to take to the range, a red dot is the way to go. There are plenty of very affordable dot sights that are reliable, long-lasting, and good enough for anything short of duty use or home defense – and if you’re willing to increase your budget, high-end red dots are perfectly capable of handling those tasks, too.

Hunting

A variable-zoom telescopic sight is going to be ideal for most hunting applications, especially in parts of the country with lots of wide open terrain. There’s also a case to be made for the other optics on this list in certain situations – if you’re hunting pigs in dense underbrush where most of your shots will be taken inside of 50 yards, a red dot, reflex sight, or holographic sight would make it easy to track moving targets and deliver fast follow-up shots.

Personal Defense

When it comes to personal defense, you’re going to want an optic designed for close quarters shooting, such as a red dot, reflex sight, or holographic sight. A reflex sight or holo sight has a minor advantage in cramped indoor environments thanks to the slightly larger field of view and the option for different reticles that aid in faster target acquisition, but ultimately any unmagnified optic that you have trained on and feel comfortable with will be a good choice – just avoid cheap optics that could risk failing on you at the worst possible moment.

SHTF

Building an AR-15 with a SHTF scenario in mind is becoming increasingly popular, and picking the right optic to pair with your rifle is an important decision. In this case, it’s best to go with something that has proven itself in some of the harshest climates and most intense combat environments on the planet – prism scopes like the ACOG and holographic sites offered by EOTech are both used by military and law enforcement the world over, and the high-end models are all but bomb-proof, as long as you can stomach the price tag.

Eye Issues

If you suffer from astigmatism, need prescription glasses to shoot, or happen to be cross-eye dominant but still want to practice shooting with both eyes open, a prism scope is the optic for you. The unique design of these optics all but eliminates blurred or double vision, and the reticle typically appears brighter and crisper to shooters with poor eyesight.

Final Thoughts

As is often the case, the best way to decide which gear is right for you is to decide what you want to do with it. The beauty of the AR-15 platform is how modular it is – whether you want a lightweight SBR with a reflex sight to use as a truck gun, or a 24-inch barrel and high-powered scope for ringing steel plates at 1,000 yards, you can rest assured that there’s a build that will suit your needs. We hope this article has given you a better idea of the differences between these optics and the different niches that they fill.

[We'd like to extend a huge thanks to Eric Shattuck for his hard work on this article! Leave a comment below and check out his other articles about 9mm Carbines and the 2022 Ammo Shortage. We sell the best value AR-15 and AR-10 rifles, uppers, barrels here at Bear Creek Arsenal; shop your next build here!]