Choosing the right height for a red dot is one of those decisions that seem simple until you make the mistake of trying to research them. Then, you’ll be treated to a whole smorgasbord of opinions, all definitively claiming that their preferred height is the one true correct one and all others are wrong.
The truth is, it’s not as crucial as much of the internet would have you believe; in most cases, if you pick one of the three most popular heights, you’ll still be able to hit the target if your fundamentals are good.
But, that doesn’t mean it’s completely irrelevant, either. Different heights were developed for different purposes, and each lends itself best to different applications.
Does Red Dot Height Matter?
The short answer is, yes, it does matter, particularly if you start branching out beyond the three most common heights, which we’ll cover a bit later. Too low of a mount, and you won’t be able to get a comfortable sight picture, particularly with a rifle with an inline stock, such as an AR-15. Too high, and you may find yourself unable to get a decent cheekweld.
Red dot height affects more than just your ability to get behind the dot, though. If you have any other accessories installed on your rifle’s top rail, you’ll have to take that into consideration. A larger IR unit—a PEQ-15 or something similar—might obscure your sight picture with certain mounts.
While tape switches and their alternatives are generally low enough that they are not a concern, the hand placement they require may be. If you have large hands, you might not be able to actuate your light or IR laser without obscuring your dot with a low mount.
Height can also come into play if you plan on using your dot with a night vision device. IR lasers can be mounted to alternative locations if sight clearance is a concern, but for passive aiming, there is only so low you can mount a red dot before it becomes difficult or impossible to get behind the dot while using your NODs.
In fact, the recent proliferation of night vision is one of the primary drivers behind the current (and growing) popularity of extra-tall red dot mounts. Other factors include a reduction in neck strain when aiming for prolonged periods, and a more “heads up” stance when using an extra tall mount, allowing for improved peripheral vision.
The height of your red dot will directly dictate your height over bore, though, and so while it may be tempting to simply go with an extra-tall mount just in case you ever get night vision or need the additional height, these mounts are not without trade-offs.
Some sights, including several Primary Arms red dots, come with multiple different mounts or risers, allowing you to experiment with different heights without having to shell out extra cash.
Choosing the Right Red Dot Height
The first thing you need to consider when selecting a red dot mount height is your minimum required height. For an AR-15, this typically means a height of no less than ~1.4″ inches, measured from the rail of your receiver to the midline of your optic. Absolute cowitness mounts (mounts which place the center of the optic at the same height as common irons sights, as opposed to lower 1/3rd mounts, which situate the optic slightly higher) will typically fall somewhere around this number.
This minimum height is required because the AR-15 uses an inline stock; that is, the stock does not drop or in any other way allow room for your head. While rifles with contoured stocks that drop from the line of sight, such as traditional hunting rifles, can get away with much lower mounts, AR-15s cannot. It would be difficult or impossible to cram your face against the buffer tube hard enough to get a decent sight picture.
So with a minimum height determined, we should next look to the maximum height, which will vary for each user. Heights of up to 2.91″ are commonly available, but that does not necessarily mean they will be comfortable or practical for your application.
Extra-tall mounts frequently compromise users’ ability to achieve a cheekweld with their firearm, instead necessitating a chin-weld or no weld at all. This reduces stability for longer, more precise shots and can slow down your ability to get behind the dot. Of course, if you require an extra-tall mount for compatibility with night vision or other accessories, these trade-offs may be worth it.
Alternatively, with some rifles, users can compensate for an extra-tall mount by using a cheek riser, thereby allowing them to achieve a proper cheekweld again. Unfortunately, since AR-15s are top-charging, adding a cheek riser to one can be challenging—though not impossible.
For those who do not have a specific need for an extra-tall mount, any mount that significantly inhibits your ability to find a decent cheekweld can be dismissed. For most users, this will be anything with a height over 1.93″, but your body dimensions may vary.
With your minimum and maximum heights determined, you can start to assess more minor considerations, such as height over bore and neck strain. Both tend to get more attention than they require but are worthy of some thought.
Height over bore refers to the difference between the midline of your optic and the midline of your barrel. It is important to note that your height over bore is different from your mount height; i.e., if your red dot is using a 1.93″ mount, your height over bore will be considerably larger than 1.93″, because that measurement is taken from the rail, not the bore. Your height over bore is an important factor in determining your ballistic drop profile, so take care to accurately record it in your ballistic calculator. Because it can alter your drop profile, it may also have an effect on your ideal zeroing distance.
The most significant effect of height over bore can be seen at very close ranges, where a larger height over bore will generally be detrimental. The larger your height over bore, the more your point of impact will shift as targets move closer than your zero distance. This can generally be compensated for with diligent training to adjust your point of aim at these distances.
Similarly, neck strain can be a legitimate reason for users to opt for a taller mount, but typically only becomes an issue after many hours of continuously using your rifle; an issue most casual users, even seasoned competitors, will never encounter. Those outfitting a duty rifle, though, may want to consider an extra-tall mount.
Red Dot Mount Options
Most red dot mounts fit into one of four categories: low, absolute cowitness, lower 1/3rd cowitness, and extra-tall. When buying a red dot for AR-15s and similar rifles with inline stocks, low mounts can generally be ignored, as we previously covered. The remaining three categories are all viable options, though, each is best suited to a different use case.
Absolute Cowitness
Absolute cowitness is the lowest mount height that is typically useful for an AR-15. Exact heights will vary between manufacturers, but absolute cowitness mounts will usually be around 1.42″ tall. This type of mount should allow backup iron sights to be used and present in the middle of the optical field of view.
Some users prefer this type of mount because it allows the iron sights and red dot to be used simultaneously. This is particularly useful for users with extensive experience with iron sights since it offers most of the benefits of a red dot with minimal retraining.
Some users also appreciate the speed with which one can transition to their backup sights if the red dot should fail; since you’re already peering through your iron sights, transitioning to them in the event of a failure is functionally instantaneous.
Absolute cowitness mounts will typically offer the most secure cheekweld, but will also require you to crane your neck the lowest to get a sight picture. This can be compensated for by raising the rifle on your shoulder—but you start to compromise your stock position. Ultimately, the right combination of cheekweld, stock position, and sight height will come down to the individual user.
Lower 1/3rd Cowitness
Lower 1/3rd cowitness offers a slight increase in height, biasing towards red dot performance but without compromising iron sight usability. These mounts are typically around 1.57″ tall, but depending on the manufacturer can rise as high as 1.7″.
As the name would suggest, a lower 1/3rd cowitness mount is designed to situate your red dot so that your iron sights can still be used, but will align in the lower portion of the sight, leaving the center area with the red dot unencumbered. By shifting the iron sights out of the immediate area of the dot, these types of mounts typically improve target acquisition speed compared to absolute cowitness mounts and obviously, clear your field of view.
Should your red dot ever fail, transitioning to your irons is as simple as lowering your head slightly. Not as instantaneous as with an absolute cowitness, but far from slow. Should you ever wish to cowitness your iron sights and red dot with a lower 1/3rd mount, you will find that your red dot does still align with your front sight post, just as with an absolute witness mount.
Most users will not have any issues acquiring a secure cheekweld with a lower 1/3rd mount, but they do still typically raise the dot high enough to clear most IR units, although the unit may still obscure some of the lower part of the field of view. Despite this, most users still find them difficult to use with night vision, as the dot may be tall enough to clear an IR unit, but generally is not easy to get behind while wearing NODs.
Extra-Tall Mounts
The extra-tall moniker was originally coined to describe 1.93″ and similar mounts, which were developed to address perceived issues with existing absolute and lower 1/3rd cowitness mounts. However, as time marches on, taller and taller mounts are growing in popularity, making many question if 1.93″ mounts can really be considered “extra-tall” anymore.
Regardless of the nomenclature, 1.93″ mounts remain the most popular of these types of mounts. This height considerably improves the ability of the user to passively aim with night vision and will clear nearly any IR device mounted to the top rail.
Unfortunately, this type of mount also typically precludes the user from being able to cowitness with traditional iron sights. Some mounts come with alternate solutions, such as the built-in BUIS in Unity Tactical’s Aimpoint FAST mounts, but in many cases, extra-tall mounts and backup irons are mutually exclusive.
Additionally, due to the additional height over bore compared to a standard or lower 1/3rd mount, extra-tall mounts will slightly alter your ballistic drop pattern. While standard and lower 1/3rd mounts can be use with common zeros such as 50/200 or a maximum point blank range zero, extra-tall mounts will often result in a more parabolic pattern. For instance, a 50m zero with a 2.26” tall mount will reconverge at around 275 yards, rather than 200.
While 1.93″ and taller mounts are gaining popularity for the reduced neck strain they offer, they do typically make it difficult for most users to acquire a cheek weld, necessitating a “chin weld” instead to get a stable and secure sight picture. Certain taller mounts may preclude users from getting any kind of weld but are typically used for CQB applications where a precise head position isn’t necessarily required.
Conclusion
As with most firearm accessories, red dot mounts are available in a variety of heights because users have a variety of needs. Those looking for a secure cheekweld and minimal change after a lifetime of shooting with iron sights will usually gravitate towards absolute co-witness mounts, while those with night vision overwhelmingly choose extra-tall mounts.
In the end, choosing the right red dot height is all about matching the tool to the job at hand.
If you still have questions about finding the right red dot and mount, check out our red dot buyer’s guide. Or, if you’ve found your new dot and gotten it mounted, our instructional article on how to zero a red dot will get you zeroed in and ready to go as fast as possible.
