After a good optic, there is no single accessory more important than a quality weaponlight. Most accessories offer small improvements to your performance—reduced recoil, a more secure grip, a more stable firing position—but a weaponlight offers a new capability entirely, enabling you to be your own light source and engage targets in any ambient lighting conditions.
To get the most from your weaponlight, though, you need to have it mounted to your rifle effectively, and with the plethora of mounting options currently on the market, figuring out how to do that can be a challenge. Before we get into the details of mounting positions, though, it’s important to understand the terminology we use to describe them.
Understanding the Clock
You’ll often hear people describe the position of their weaponlight using time, such as 3 o’clock or 9 o’clock. This refers to the position of the light axially relative to the barrel.
To understand the positions, hold your rifle in a normal firing position, then imagine a clock on the muzzle facing toward you, with your firearm’s barrel at the precise center. The position of the hour hand at the stated time indicates the position of the weaponlight.
Using this system, the axial position of a light can be easily described, even if the position is unorthodox. 12 o’clock would indicate that the light is mounted to the top rail, where you would normally find iron sights and optics, while 6 o’clock would denote a light mounted to the very bottom of the handguard.
While top- and bottom-mounted lights could be easily described without clockface indices, other positions would be more difficult without them. A 2 o’clock position, for example, would put the light at an angle between the top and side rail on the right side. A 1 o’clock position would also fit that description of being between the top and side rail, but by using the clockface descriptors, we know that position is incrementally closer to the top rail.
Where is the Best Place to Mount a Flashlight on an AR-15?
With that out of the way, we can meaningfully talk about the best way to mount a weaponlight on an AR-15. The best position for you will be a function of three separate but interrelated variables: position on your rifle’s handguard, clockface location, and ergonomics.
How Far Forward Should You Mount a Weapon Light?
Light position tends to be the first question users have when they start considering how best to mount their weaponlight. Depending on the model of your handguard, you may have nearly limitless space to mount your light.
Luckily, the answer is pretty straightforward in most scenarios: just mount your light as far forward on your handguard as is practical for your setup.
What is practical will vary depending on your needs and preferences. For instance, if you intend to use a tailswitch to activate the light with your thumb, then there will be a limit to how far forward you can situate your light relative to your hand position. If your hand position is limited by another accessory, like a bipod, this combination may require you to mount your light further rearward than would otherwise be ideal.
As a rule, though, you should mount your light as far forward as you are able, without causing the front of the light to protrude past the muzzle. Situating the light forward of the muzzle adds unnecessary extra length to your setup and offers no advantage compared to having your light flush with the muzzle.
The reason you want your light as far forward as possible is because of shadow. Every light source casts one, and your weaponlight is no exception. In this case, the primary shadow will be created by your barrel and possibly your handguard, because they are the closest opaque objects to your light.
Barrel shadow is non-ideal and should be minimized because it limits your ability to observe your environment. It creates a dark spot in the field of light generated by your weaponlight–one in which anything could be hiding. By mounting your light as far forward as possible, you minimize the barrel shadow, creating the widest possible arc of illumination.
Which Side Should You Mount a Weapon Light On?
Which side to mount your weaponlight on primarily comes down to how you’ll use it.
For a light that is directly activated with a tailcap button, you’ll usually want to position the light on the non-dominant side of your rifle– so for right-handed users, you’d mount the light on the left-hand side of your rifle, typically somewhere between 9 o’clock and 11 o’clock. Left-handed operaters would do the opposite, placing the light between 1 and 3 o’clock.
This location allows you to easily actuate the light by slightly moving your non-dominant hand and stretching your thumb forward to work the tail switch.
Alternatively, if you use a remote switch, you’ll want to do the opposite. A right-handed user will typically want to mount the light on the right-hand side of their rifle between 1 o’clock and 3 o’clock. This will free up space on your rifle’s handguard so that you can grip your rifle as far forward as possible.
In either case, you’ll want to position the light high on the rifle rather than low. By locating the light in the upper right or left quadrant of the rifle, you cause the barrel shadow to be cast down and to the opposite side, which typically obscures less of your field of view than mounting the light low and casting the shadow high.
Pressure Switches
Of course, if you’re using a pressure switch, you’ll likely wonder where to mount that as well. The answer to this question is more nebulous; while there are a number of common locations for a pressure switch, there is really no single right spot.
Ideally, you want your remote switch to be easy to actuate with minimal adjustment to your firing grip. But, it should also usually not be located directly underneath your thumb in a normal firing grip, in order to avoid unintentional activation.
For example, if you operate your rifle with a typical C-clamp grip as far forward on the handguard as possible, then a good location for the remote switch to your light might be slightly forward of where your thumb naturally rests in this grip on the top rail. In that position, you would need only to slightly move your thumb in order to engage your light.
Unfortunately, that’s frequently where your front sight is located; or, if you truly grip your rifle all the way forward on the handguard, there may be no rail space located in front of your thumb. In either scenario, a second option is to mount the switch on the upper left 45-degree section of your handguard for common seven-sided MLOK handguards or on the left-hand rail for Picatinny designs.
Either of these locations requires only a slight adjustment to your firing grip in order to actuate–basically, switching from a full C-clamp to a partial or to a traditional undergrip. While less ideal than the original switch position, both are highly functional and perfectly viable for most users.
Weapon Lights and Muzzle Devices
One common objection to locating your weaponlight all the way forward on your handguard is its proximity to your muzzle device.
In the case of devices like muzzle brakes and flash hiders, the force from expanding hot gasses created by firing and the impact of unburnt powder particles can be a source of concern, but in most cases, the danger is negligible. High-quality weaponlights are designed to withstand these forces, and should not be permanently damaged.
However, situating a light very close to a muzzle brake or flash hider will commonly cause carbon buildup on the light, sometimes to a degree that will cause a notable reduction in light output after a few hundred rounds. Like most built-up carbon, this can be removed with a gentle cleaner like CLP, but may require some elbow grease.
To reduce cleaning times and make it easier to clear your light’s lens in the field, you can use protective stickers or a coating agent like petroleum jelly or chapstick. Stickers can easily be peeled and replaced when they become cloudy, saving you from having to clean your actual lens, while petroleum jelly or chapstick are easily wiped off and reapplied, preventing the carbon from caking on.
A less common, but no less valid, concern involves suppressors. Due to their unusual size, suppressors can create significantly larger barrel shadow if your light is mounted flush with your muzzle.
If you frequently shoot both with and without a suppressor, there is little that can be done to avoid this, but for rifles dedicated to suppressed use, you can minimize shadow by using a cantilever or extended light mount to shift your weaponlight even farther forward. In this case, you can essentially treat the end of the suppressor as the muzzle, even if it is not permanently attached, and mount your light as close to it as possible.
Conclusion
Weaponlights are an important piece of hardware for any firearm that even might have to be used in the dark.
When mounting your light, situate it as far forward as possible to minimize barrel shadow, and try to position it high on your rifle rather than low to cast the shadow down instead of up. However, it’s important to keep in mind the ergonomics of how you will actuate your light, which may require a slightly more rearward position in some cases.
