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The Nuts and Bolts of Thermal Weapon Sights

Mounting a thermal scope or clip-on to your AR-style rifle is an easy proposition

November 13, 2017  |  by Brent T. Wheat

Primary thermal targeting systems like the Armasight by FLIR Zeus Pro mount quickly to bolt-action rifles with a factory rail. Short Picatinny rails are readily available for most modern bolt guns if yours didn’t come with one.
Primary thermal targeting systems like the Armasight by FLIR Zeus Pro mount quickly to bolt-action rifles with a factory rail. Short Picatinny rails are readily available for most modern bolt guns if yours didn’t come with one.

After the seemingly endless administrative gymnastics of research, justification, documentation and a bit of strategic grousing, that long-dreamed-of thermal sight has finally arrived.

The first order of business is getting that sight firmly affixed to the top of your rifle, but because thermal sights are still relatively new outside of the armed forces, there aren’t many people available to help set up your new gear. Read on and we’ll try to close that knowledge gap, so you better understand the mounting options available to you. With a bit of thought and planning, you’ll soon be outside and sending rounds downrange.

Mounting a thermal weapon site like FLIR’s new ThermoSight Pro PTS233 as the primary targeting device is an easy proposition for any firearm with a standard Weaver or Picatinny (MIL-STD-1913) rail. Simply attach the sight to the top of the rail, check for proper torque of all fasteners, correct eye relief, and then head to the range.
Mounting a thermal weapon site like FLIR’s new ThermoSight Pro PTS233 as the primary targeting device is an easy proposition for any firearm with a standard Weaver or Picatinny (MIL-STD-1913) rail. Simply attach the sight to the top of the rail, check for proper torque of all fasteners, correct eye relief, and then head to the range.

Most thermal sights utilize a quick-detachable mounting system that is designed to interface with either a standard Weaver or Picatinny (MIL-STD-1913) rail. The incorporation of a quick-detach base allows flexibility in mission planning, as your new investment could be used as a handheld thermal imager in addition to its primary role as a weapon sight. A rail mount is the way to go if you want such ability.

There are two main types of thermal weapon sights: primary, standalone targeting devices, and forward-mounted thermal imagers intended to augment existing day sights.

Primary thermal imaging optics will have an electronically adjustable reticle in the image field, just like a standard telescopic sight, though most incorporate a variety of user-selectable indicators ranging from standard crosshairs to Mil-Dot and ranging types. Forward-mount thermal sights may not have a reticle. If they do, it is usually switched off, as not to conflict with the shooter’s perception of the daytime optic.

Add-on thermal imagers like Armasight by FLIR’s Apollo Pro require real estate in front of the primary optic. This is not a concern for most AR platforms and MSRs, many of which come equipped with a long rail. It is a simple matter for an armorer to install an aftermarket full-rail fore-end if your rifle isn’t so equipped.
Add-on thermal imagers like Armasight by FLIR’s Apollo Pro require real estate in front of the primary optic. This is not a concern for most AR platforms and MSRs, many of which come equipped with a long rail. It is a simple matter for an armorer to install an aftermarket full-rail fore-end if your rifle isn’t so equipped.

While primary thermal targeting systems are highly accurate, there is potential for a point-of-impact shift anytime the optic is moved on and off a weapon. With a well-made mount this error is nearly imperceptible, especially in close to medium-range engagements, but in tactical missions, any potential shift raises concern for the precision marksman.

There is no such concern with a forward-mount thermal imager. Since these utilize the reticle in the daytime optic for aiming, there is no change in the point of impact when introducing the thermal imager into the visual chain. Of course, each weapon system is different and needs to be tested extensively prior to critical use. For the most part, however, a forward-mount thermal imager is a simple matter of “use it when you need it.”

Either type of system can be permanently mounted on the weapon to remove any doubt and leverage the 24/7 benefits of thermal imaging, so weigh the pros and cons of fast detachment versus more permanent solutions before moving forward.

This rifle is equipped with an integral rail on the barrel. If yours doesn’t have one, a gunsmith can add a second short rail to your bolt-action rifle to facilitate easy-on-and-off of a forward-mounted thermal device.
This rifle is equipped with an integral rail on the barrel. If yours doesn’t have one, a gunsmith can add a second short rail to your bolt-action rifle to facilitate easy-on-and-off of a forward-mounted thermal device.

There are three primary ways to mount a thermal weapon sight. The first is by utilizing the stock rail on the weapon. The most commonly seen example is a “flat-top” AR-style rifle.  You simply attach the sight to the top of the weapon, check for proper torque of all fasteners, correct eye relief, and then head to the range.

Many other weapons systems can utilize a rail, including bolt guns. There are several after-market manufacturers who build bolt-on long rails for popular bolt-action rifles. If you can’t find a bolt-on replacement for your particular gun, you can always employ the services of your friendly neighborhood gunsmith.

Forward-mount sights can be a little more challenging because rail mounting requires real estate in front of the objective lens of the primary scope. An AR-platform rifle is perfect if it has a fore-end that incorporates a full-length rail; such rifles are available from many major manufacturers. It is also a simple matter for an armorer to install an aftermarket full-rail fore-end.

FLIR’s FSRS (Front Scope Rail System) mounts on an existing rail and provides scope rings plus an extended rail forward of the day optic. This is a great DIY solution for adding a forward-mounted thermal imager, especially for hog and predator bolt guns.
FLIR’s FSRS (Front Scope Rail System) mounts on an existing rail and provides scope rings plus an extended rail forward of the day optic. This is a great DIY solution for adding a forward-mounted thermal imager, especially for hog and predator bolt guns.

Bolt guns can also have a longer rail installed to accommodate a forward-mount thermal imager, but many users opt for a separate, smaller forward rail on the barrel. It’s also possible to install a mount that attaches to the stock fore-end and skirts the barrel without touching it. Any of these types of installations require the services of a qualified gunsmith.

A DIY option is to go with a proprietary forward-mount like the FSRS (Front Scope Rail System) from Armasight by FLIR. This mounts on an existing rail and provides scope rings plus an extended rail forward of the day optic. These are simple, well-engineered solutions and can work well if your weapon already has a short rail. Couplers are also available that are designed to attach a forward-mounted thermal imager directly to the objective ring of the daytime scope.

Certain thermal add-on devices can simply be coupled directly to the objective ring of the primary optic.
Certain thermal add-on devices can simply be coupled directly to the objective ring of the primary optic.

Thermal imaging technology is quickly being adopted by civilian law enforcement agencies because of the literal “sixth sense” it provides. Thermal scopes like those in FLIR’s new ThermoSight Pro Series epitomize thermal technology and excel as a primary weapon sight because they perform in any lighting conditions. Meanwhile, clip-ons add powerful thermal capability to virtually any platform employing a daytime optic. Mounting these optics is a simple matter and shouldn’t stop any shooter from experiencing their benefits.

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