r/DigitalNightVision

#GRL335 Thermal Optic Review

The GRL-335 mounted to my CZ600, with shooting bags for testing.

#Specs

Objective lens: 35mm
Magnification: 4x (base), 8x, 12x and 16x digital zoom.
FOV: 6.5 degrees.
Detection range: 1800 Meters / 1968 Yards.
Eye Relief: 50mm / 2 Inches.
Diopter Adjustment: +5/-5.
Focus Range: 3m to infinity.
Battery: 18650 Cell.
Weight: 635 Grams / 23.4 Ounces (with battery)
Maximum recoil force: 1000g per 0.4ms / 17 ft/lb (A moderate .308 load, roughly)

#Introduction

The GRL-335 is a 4-16x thermal scope made by GOYOJO. I recently acquired one and wanted to write a review of my experiences with it for you all, and hopefully it proves useful, or at the very least, interesting to you all. I've done my best to break down as much detail as I can, and as a result it's quite wordy. If you have any specific questions for anything I may have missed, please feel free to ask and I’ll answer as best I can.

#Packaging/included items

The GRL-335 comes packed in a zippered semi-hard case, nestled in a form-fitting flocked cavity. While I’ve seen this type of zippered case a few times from overseas manufacturers, I think this is the first time I’ve seen it with the flocked insert. It’s a nice touch, and the case itself is rather handy and sturdy.

The outer cardboard box is even surprisingly sturdy, and has magnetic clasps holding it closed that feel more like you’re unboxing a nice phone or something than a rifle accessory. Again, it’s a nice touch and a little more premium-feeling than what I’ve gotten from other optics manufacturers. Arken and Bushnell could both step it up a bit in that regard, heh.

Included in the case with the GRL-335 are:

An 18650 charger with USB cable and wall adapter
An alternate, longer rubber eyecup
A USB cable for the GRL-335 itself
An offset mounting plate should you need to mount it further back than your available picatinny rail will allow
A cleaning cloth

The included items.

The GRL-335 nestled in its' case

#Design & Ergonomics

The physical design and aesthetics of the GRL335 immediately struck me as “ACOG-Adjacent”. I think GOYOJO had the Trijicon ACOG in mind when doing the design for the outer shell, right down to the orientation of the battery compartment to emulate the adjustment knobs of their muse. It’s a little larger, and clearly has some obvious specialist elements that set it apart (the mirror-like finish of the germanium objective lens is a dead giveaway) but it’s recognizable. The result is something that looks at home on pretty much anything an ACOG would, which is kind of nifty.

The design’s overall preference for rounded shapes help keep snags to a minimum, with the exception of the battery compartment, which does jut out a bit. The overall design of the unit, while larger than an ACOG, is quite compact for a device that can provide 16x magnification, even if it is digital. It also weighs in at 635 grams, which is on the lighter side when compared to conventional 4-16 optics.

The outer shell itself is made from cast aluminum, and feels quite robust. At first glance, it might seem a little chunky, but it makes sense given the application - Thermal optics need a way to effectively dissipate the heat generated by the infrared detector array, and this is traditionally done via thermoelectric cooling wherein waste heat is shunted towards a conductive heat sink, typically using the peltier effect. In this case, the heatsink is the aluminum outer shell of the GRL335. It does a superb job, and during extended use the optic never got much more than slightly warmer than ambient.

The battery cap is a sturdy aluminum cap that screws onto brass threads. It feels decently heavy-duty and I have no concerns about the threads stripping like I would with a plastic cap or housing. The battery used is a standard rechargeable 18650, which means it’ll be very easy to source, and if you’re the type to be looking into thermal scopes, odds are you probably already have a few for other gear. One is, however, included.

The controls for the GRL335 are on the top of the optic, and are very straightforward. There are four buttons: Zoom in, Zoom out, Menu, and Power. These buttons are multi-function, and serve as navigation and enter/back buttons when navigating the menus. Holding down the zoom in button will activate picture-in-picture mode, allowing you to have both the 4x and 8/12/16x at the same time. The controls are quite simple, but not at all in a bad way. It just works.

The manual focus/parallax adjustment is located on a notched blue-anodized ring at the front of the device. It’s large, and easy to operate without looking up from the optic. I found it perfectly natural and easy to make adjustments while shooting. The parallax on the optic is pretty forgiving, and mostly serves to provide additional detail for better target identification and image fidelity. Due to the amount of contrast the thermal imaging provides, I think you’d be able to roughly identify even out-of-focus targets with relative ease, provided you’re sufficiently familiar with the species present within your hunting grounds.

In front of the parallax is the germanium objective lens, which sports a DSLR/Digital Camera-style lens cap on a retention strap. This works well to protect the objective when not in use, and comes off quietly and easily, but you’ll need to be careful if your firearm has a charging handle or bolt on the left side, and to keep it from rattling. You could easily swap the retention lanyard (and by extension what side of the rifle the cap hangs on when not in use) with a small hex key if necessary, or remove it so that you can just pocket the lens cap. In some ways, I sort of wish that it were possible to use a conventional riflescope flip cap.

The GRL-335 mounts up using a pretty standard lever-actuated quick-detach mount. The QD functionality is nice, as it means the optic can be easily removed from a rifle or kept at the ready in a padded pouch to be used as a handheld monocular, so you have the ability to thermally glass an area in a safe manner. From my experience, it has a pretty secure hold on the pic rail, and does the job. It’s perhaps not as nice as my ADM mounts, but it’s a pretty solid piece of what appears to be CNC milled aluminum, so it feels well-built and has a beefy recoil lug.

#Features & Interface

The GRL-335’s interface may take a little getting used to at first, mostly due to the fact you’re only using four buttons. That said, if you spend a few minutes with it, you’ll quickly realise that it’s not terribly dissimilar from a digital camera - which makes sense, because it pretty much is one. In that context, it’s quite straightforward. Without going into perfectly granular detail on every menu, which would likely make this section excessively long, these are the main points covering the most frequently used menus:

The primary menu button - marked with a prominent “M” - opens the device menu when held down, and cycles through various color palettes when quickly pressed. These are:

Red Hot
White Hot
Black Hot
Iron Red
Green Hot
Fusion
Ice Fire

Example Video

shows color palettes, as well as different magnifications and detection ranges in the case of people in the background.

The different color palettes offer a nice variety for the user’s preferred tastes, although they tend to be situational. Certain conditions and environments look a little better through certain ones than others to my eyes, and vice versa, due to the way the visual information is represented by specific palettes. Whether or not they’re actually functionally more effective, I’m not sure, as it’s all the same data in the end - but I find some palettes easier to visually parse under certain conditions, so I find myself flipping between them as needed.

Quick-Pressing the power button will open up a menu allowing you to select from either a photo or video, and pressing it again will either take said photo or begin recording a video onto the installed microSD card. The ability to record is certainly a nice feature, and it can be set to record upon detecting recoil as well. The recording quality itself is decent, though compression is evident. I’m told that GOYOJO is working on an improved version of the GRL-335 with better-quality recording and audio, though, which will be a nice update. The recordings and photos are viewable under the “Playback” item in the onboard menu.

Zeroing the GRL-335 is done through the zeroing menu section, and usually consists of taking a shot at the bullseye of a target or similar reference point and then keeping your reticle on target while activating the zero function in the menu. You then place the indicator on the actual point of impact, and confirm it. You also set your zero distance. That’s it - if your target is sufficiently visible, it’s a one-shot zero. I like using rubber targets for this purpose, as they show up well under thermal devices when hit. As an aside, livestock stall mats cut and attached to target stands work great as thermal targets.

There’s a few reticles to choose from as well, including a specific 6.5 Creedmoor reticle, no doubt due to the round’s popularity these days. Some of them are simple duplex or holo-style reticles, but I think my favourite overall is the dynamic BDC simply called “Shape 5”. It's a fairly simple ranging reticle that I believe adjusts to MIL or MOA based on what you have selected in the settings, and seems to adjust to emulate a conventional first focal plane. You can also choose the color of the reticle, though I most often leave mine either red or white depending on what color palette I find myself using most often.

I think it would be neat to somehow allow users to upload custom reticles to the SD card, though I’m not sure how much work that would be for GOYOJO to implement. Making your own BDC for your personal handloads would be a very nice feature, and one I don’t recall seeing elsewhere. If any of their engineers ever read this, it'd be greatly appreciated for tinkerers like me.

Another neat menu item is the ability to save presets of your settings - what they refer to as “User Data” in the menus. These effectively allow you to set up different “save files” if you will for different rifles. I can set up one for my TM-22 and one for my CZ600 Trail, and just load up the corresponding preset file as required when I transfer the optic between rifles, or you could theoretically do the same for different bullet weights. I didn’t see the ability to name the slots, so you may want to write down which one belongs to which rifle or use case. Having the ability to somehow name the slots would again be a very nice feature that currently appears absent.

#Testing & Technical Performance

I ran the GRL335 through its paces using three rifles: A 22LR carbine, a 7.62x39 carbine, and a .308 rig aimed at more precise shooting.

I was particularly curious as to how the quick-detach mounting system would hold up under recoil, and whether it would effectively return to zero once uninstalled and reinstalled, and whether it would hold zero under various amounts of recoil.

As can be expected, it performed admirably on the 22LR. This was honestly my favourite setup, oddly enough, as CCI Subsonic and Eley Subsonic acted essentially like tracers through the thermal optic, which was a ton of fun. I had sent a few hundred rounds downrange with the GRL-335 because it really was extremely enjoyable. The magnification range and default reticle worked spectacularly well for this particular rifle setup, which consists of a Derya TM-22 Pro that has seen a lot of customization and sports a 16” barrel. It was extremely intuitive at all ranges out to 120 yards, and I could see this being an extraordinarily effective small game-getter given how well it picks up little critters.

TM-22 with GRL-335 mounted

The 7.62x39 performed well too. This rifle, a CZ600 Trail with another 16” barrel, has a little more recoil than most intermediate caliber hunting rifles due to its’ small stature and short barrel, but the GRL335 had no issues whatsoever keeping up. After the initial zeroing, round after round went exactly where I expected them to. I was using surplus chinese steel-core ammunition for the bulk of the testing, which through this rifle will generally group at about 1.5-2MOA using a conventional optic. I’ve put about four thousand rounds of it through this rifle, and it’s very consistent. The GRL335 behaved exactly as expected with all shots landing right around the 1.5 to 2MOA mark. I sent around two hundred rounds downrange with no issues or performance problems. Using handloads consisting of 123gr Hornady SSTs over a load of H335, it was right around 1MOA at 100 yards, again, exactly where I’d expect for that load. I have full confidence the optic would perform well out to the maximum effective range of the cartridge.

CZ600 Trail with GRL-335 mounted

My .308, a Tikka T3X CTR in a KRG bravo chassis with a 20” barrel, is where the GRL335 began to have some problems. In all fairness, this rifle, by my napkin math, is actually above the recoil rating listed in the specs. The barrel loves heavy rounds, and heavy rounds love causing recoil, and this rifle eats a particularly stout load of a 178gr ELD-X over a hot pile of Varget. I would estimate the recoil to be in the neighbourhood of 17.8 to 18.5 ft/lb. It’s punchy. The GRL335 had difficulty maintaining a zero with this rifle, so my testing with it was limited. I don’t hold it against it, though - again, it’s more than the optic is actually rated for, if my math is right. I’m sure a semi-auto rifle or a bolt action utilizing a lighter load (perhaps around the 130-150gr range) would perform better. I intend to try a high-velocity 130gr load in the future, at which point I’ll likely revisit the GRL335 on this setup. 6.5CM would probably be fine too, with its lighter recoil.

The GRL-335 mounted to my Tikka T3X CTR.

Return-to-zero testing was done on both the TM-22 and the CZ600 Trail, and consisted of removing the optic using the quick-detach mount and reinstalling it using the standard procedure for QD optic mounts: Ensuring both mating surfaces are clean, putting the optic in the same position on the rail each time, applying forward force to seat the recoil lug properly, and tightening the QD lever. Care was taken to ensure that the QD mount was appropriately tight beforehand, and it was not adjusted once initially set, which would affect zero. I repeatedly removed the optic, reinstalled the optic, and took a series of five shots.

On both rifles, I had no problems regaining a functional zero each time. There was some variance with each group, and there often is until you start getting into QD mounts that cost about half of the GRL335’s entire price (such as the ADM Recon/Delta series, which I’m particularly fond of) but each group was within an inch where I expected it to land at 100y. If you’re going to be removing your optic and need better accuracy than that, you should be verifying your zero anyway, which is easy enough to adjust using the GRL335’s one-shot zero function.

For practical accuracy/use purposes, that 1MOA variance at a hundred yards is well within the threshold of what I would consider acceptable for my use cases on these rifles if I needed to remove the optic in the field. Besides, I always verify my zero prior to a hunting trip - and you should, too.

#Detection range & Image Fidelity

The GRL-335’s image fidelity is impressive for a thermal at its’ price point. Obviously, thermal optics trade overall image quality for the ability to see infrared radiation, and are limited by their sensor grid size. In the case of the GRL-335, that’s 384x288. It’s not exactly the hubble telescope, but it’s perfectly serviceable at intermediate ranges. Compared to higher end thermal optics, the difference in image detail is quite noticeable, but the GRL-335 is also noticeably cheaper than most.

That’s another trade-off when it comes to thermals: sensor resolution and cost are more or less directly correlated. The similarly sized Nocpix Slim H35, for example, has a sensor grid resolution of 640x512 - but it also costs $3500CAD. Other than the sensor resolution, its feature-set is very similar, with the thermal cores both being 12-micron, 50Hz (though the GRL-335 actually lists 55) and relatively similar NET-D ratings (18 for the Nocpix, 25 for the GRL-335). The GRL-335 is currently $1300CAD, so the difference in sensor resolution and sensitivity equates to $2200 on the price tag. While the lower resolution does limit the GRL-335 in some ways, I'm willing to take that trade-off.

GOYOJO lists the detection range at approximately 1.8 kilometers on their spec sheet, though I was able to identify human-sized heat signatures as far as two kilometers in ideal conditions. The identification range is significantly shorter, and it varies based on what you’re looking at and what detail you’re looking for. If you have multiple species of small ungulates (for example, various deer) in your region, that’s tricky - you’d have to be quite a bit closer or use the GRL-335 for initial detection and then confirm the exact variety of critter with a conventional or night vision optic. If you’re looking to identify a species that has no similar ones in the area - for example, moose or wild boar in most locales - it’s much easier, as their profiles are much more distinct and readily identifiable.

Similarly, for airsoft or similar tactical-style use, it would be the same sort of situation. Humans are very distinctly shaped, and as long as you have context clues (for example, the direction the opposing force is approaching from or the location of any friendly entities) targets can be identified using basic deduction and communication.

The image fidelity is sufficient in either case that within 150 meters, positive identification of targets is relatively easy using purely image quality. For larger game, that would stretch out further. Inversely, if you’re hunting small game, you’re going to need to bring it in a little if there are lookalikes. If you’re hunting rabbits and squirrels and such, you’re likely not shooting too far anyway, unless you’re using a purpose-built varmint rifle. It really is a bit of a “your mileage may vary” situation based on your exact use case, though, and I can see some people getting frustrated if they have to identify similar-looking animals or targets in less-than-optimal conditions. It's certainly something you should keep in mind.

An example of the recording through the optic, firing 22LR into rubber livestock mats (which work well for thermals)

Note: The image quality is compressed. Target is at 60 meters.

I’m inclined to say that the GRL-335 will likely fall into the hands of hunters the most, who (at least, in my case) are unlikely to take a shot on live game at extended distance in most cases with a budget optic. With the correct rifle setup, you absolutely can stretch out into long distance hunting, but it’s generally rare for most due to a combination of terminal ballistics, terrain and rifle limitations, and generally requires a purpose-built rifle. Most of my typical hunting shots are 150 yards or less, especially deer, due to the terrain limitations in the Pacific Northwest’s mountains and forests. At that distance, the GRL-335 works for me.

#Overcoming conventional visual obstructions - And suffering from a few thermal-specific ones.

Thermal optics, including the GRL-335, have some advantages and disadvantages related to environmental conditions that I think are worth talking about. Most of this section isn’t specific to the GRL-335, but I figure it might be useful to people who haven’t used thermals before. Those of you familiar with them might see it as stating the obvious - I won’t blame you if you scroll through and skip it.

While I imagine most of you are already aware of this, thermals are not affected by the dark, meaning they act as a sort of night vision by default provided there’s enough of a contrast in the temperature of your surroundings. It won’t have the same optical fidelity as modern night vision due to the limitations of thermal sensor resolutions, but it’s still useful. Heat signatures will be a little easier to spot at night as well as the environment cools without the sun’s heat, making targets pop a little more.

When it comes to atmospheric or weather conditions, particularly things like fog, heavy rain and snow, image quality can be degraded somewhat. Cool water vapor suspended in the air is an excellent blocker of infrared radiation, but generally speaking, you’ll still be able to see your targets much further than with the naked eye in the same conditions.

Some weather, snow specifically, can complicate matters as it’s an excellent insulator. Heavy snow will degrade thermal image quality more than fog, and animals’ fur already insulates them somewhat, especially if they have a heavy coat. When you stack slow-melting snow on top of that fur it works as particularly effective camouflage. Their primary heat-exchanging surfaces (the ears and face) will still absolutely glow through the GRL-335 or similar optics, but they’re directional - if faced away, you may have a hard time distinguishing them from the surrounding snow. Luckily, if any wild animal hears you or is otherwise aware of your presence, odds are they’re going to be staring directly at you.

There are some terrain features which I’ve noticed cause the GRL-335 some trouble, though situationally. The primary one is large rocky outcrops on a particularly sunny day. As you can imagine, the rock tends to absorb a lot of heat from the sunlight, which causes a bit of a washout effect when looking through the optic. It isn’t that it can’t detect anything, but rather that a large line of boulders appears as a giant hot-spot - because it is. If your quarry happens to have an outer temperature near what the rock has baked itself to in the sun, they’re going to be difficult to identify. This isn’t terribly inconvenient, as again, it’s highly situational. It requires both specific weather and terrain to be an issue - but it might be something to keep in mind if you’re using it in terrain where it might arise.

On the opposite side of things, thermal optics like the GRL-335 are particularly effective at cutting through most deliberate camouflage in a tactical situation. Camouflage clothing, conventional ghillies, and deployed smokescreens of the types encountered by airsoft players or civilians won’t do much at all against it. Specifically designed multi-spectral camouflage garments will, but they’re rare to encounter, and expensive.

As you can imagine, being able to effectively nullify conventional visual camouflage is a pretty significant advantage.

#Final Thoughts & Conclusion

The GRL335 is built as a jack-of-all-trades sort of device, in my eyes. This design approach has both benefits and drawbacks. It excels at general use, but those looking for a specialist optic, particularly for extended range use, may experience mixed results.

The magnification range makes it comfortable to use as a generalist four-power optic, but the higher digital zoom levels allow for medium distance work with relative ease or long-range observation. The compact nature of the device (again, relatively speaking compared to conventional optics of similar magnification) mean that it fits well on smaller rifles where the slightly increased weight over a conventional low-zoom optic like an ACOG (probably the best comparison given the physical similarities) would have a particularly minimal effect while benefitting most from the overall footprint and capabilities it brings.

I intend on running it on my shorter-barrel carbines (by Canadian standards - think 16” 7.62x39, .223/5.56 or a .308 running light 130gr TTSX loads) as it feels like it totally belongs there. The typical engagement distance for my carbines is 100-300 meters, well within the effective detection and identification distance for most of my use cases, and the recoil impulses of those rifles are well within the limit of the GRL335’s specs. I find that I quite like using it in conjunction with a 45-degree RMR mount sporting a Primary Arms RS10-R, as that allows for quick close-up shots (where the benefits of a thermal are minimized anyway) while the 4-16 thermal does the rest.

Oddly, I find it an absolute blast to use on a 22LR, though it is admittedly overkill for that. If you’re somewhere where thermals are legal for hunting small game, or perhaps someone doing pest control work or small game hunting at relatively close range, it would be absolutely perfect and extremely effective.

Ultimately, the GRL-335 isn’t the ultimate thermal optic - I don’t think it’s trying to be - but at the price GOYOJO is asking and the performance it delivers, it represents a solid offering and a hard-to-beat entry-level priced option if it fits your use case. I’m certainly happy with mine.

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