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REVIEW: Holosun 503 GU
There's no denying it, when it comes to micro sights, Aimpoint is the top dog. While other manufacturers have tried to compete by releasing products, so far the small Swedish company has remained dominant. The Aimpoint Micro is now available in its second generation (Here are the differences between the Aimpoint Micros: both as H2 (hunting version) and T2 (military version). The devices are almost identical, but the Hunter series does not have night vision compatibility and is only waterproof up to 5 meters (the T series is waterproof up to 25 meters). The Swedes do charge a pretty penny for these devices, with an H2 costing around €550, and the T2 devices priced at just under €800. That's a lot of money for a compact reflex sight – there must be alternatives available...
The alternative comes from Holosun, based in southern California, USA. Since 2013, the company has been producing reflex sights in Aimpoint sizes, aiming not to copy but to continuously improve the product. Holosun has a whole range of reflex sights in its lineup, differing in battery placement, mounting compatibility, and reticle options.
The latest series is the 500 series, from which we tested the 503 GU version. The "G" stands for external battery housing, and the "U" for protected adjustment turrets. While in the 400 series you had to choose between a Dot and Circle Dot reticle, all devices in the 500 series have both reticles. This means you can switch between a 2 MOA Dot for precision shooting and a 65 MOA Circle Dot for rapid target acquisition.
Brightness adjustment of the reticle is done with a plus and minus button located on the top of the housing. In the 503 CU (solar) version, the buttons are on the right side (in the direction of fire). The device has 10 daylight settings and 2 night vision settings, covering every lighting factor. Holding the minus button for 3 seconds switches the reticle between Dot and Circle Dot, or vice versa. Pressing both buttons simultaneously turns off the device. To turn it on, simply press one of the buttons, with the 503 GU reactivating in the last brightness setting.
But you can safely ignore turning it off. The Holosun comes with a battery life of 20000 hours on setting 6 Circle Dot or 50000 hours on setting 6 as a red dot with just one CR2032 battery. It also has a motion sensor that turns the optic off after 10 minutes of inactivity and back on with the slightest movement, preserving battery life.
The housing is made of robust aluminum, providing ample protection, as extensively tested in the video. The dimensions are 66mm x 64mm x 37mm, bringing the Holosun 503GU to roughly the same size as the Aimpoint H2/T2 (62mm x 41mm x 36mm). Weighing in at 85 grams without the mount, it is slightly lighter than its Swedish counterpart at 92 grams. Waterproofing is rated at 1 meter, but our tests showed no negative effects even at 3.80 meters for 30 minutes, thanks to the nitrogen filling that prevents water and humidity from entering, following the IP67 standard.
The operating temperature of the device is between -10°C and 50°C, with a storage temperature of -40°C to 70°C. Aimpoint has the edge here with an operating temperature of -41°C to 71°C and even a storage temperature of -51°C.
When it comes to mounts, Holosun includes 2 straight from the factory: a flat mount and a 1/3 lower co-witness. Aimpoint only includes the flat mount, but it can be raised to co-witness or 1/3 lower co-witness with an additional riser. The great thing about Holosun mount attachments is that they are 100% compatible with all common Aimpoint mounts, providing a wide variety of high-quality products, such as the Scalarworks LDM Micro (https://scalarworks.com/optic-mounts/ldm-micro/) mount seen in this review.
The adjustment turrets are protected by elevated material on the housing, making it quite fiddly to unscrew, but in general, once you set up the red dot sight, you rarely have to adjust it again. To adjust the zeroing point, you unscrew the caps and use them as a tool, as they have a designated slot and the markings are located on the inside of the cap. Adjustment is done in 0.5 MOA increments, providing precise and repeatable results.
Optically, the 503 GU is on par with the market leader in the current generation 2 and even better than the H1/T1 series. It provides a clean and clear image, with a precisely defined dot that is easily visible even in bright sunlight. When a magnifier is attached behind the sight, the dot remains sharp and doesn't blur, as often happens with cheaper sights.
It's worth mentioning the behavior of the red dot in combination with iron sights. Due to the angled lens in both Aimpoint and Holosun sights, there will be a deviation in the point of impact when using iron sights through the red dot sight (assuming the iron sights have been zeroed separately). The best practice with a micro red dot is to align the iron sights to the dot and use them in case of primary optic failure. Alternatively, with a quick-release mount, you can remove the reflex sight and operate without it.
We extensively tested the Holosun over the past few months. It was used regularly for precision shooting at 25m, 50m, and 100 meters, accompanied us during magnifier tests, and was used with .223 and .308 calibers. Through all these tests and frequent weapon changes, constant adjustments, checks, and shooting – the Holosun handled it all without a problem. The point of impact did not change, and the device performed as expected.
To top it all off, we pushed the device to its limits. Our attached video shows impressively that the manufacturer's specifications are not just talk, as the device works flawlessly in subzero and high temperatures, underwater (even nearly four times deeper than rated), and even after significant falls. While the housing did sustain some damage, as would be expected with any aluminum housing under these conditions, the only damage the device suffered besides cosmetic issues was a broken mounting screw and a slightly harder-to-open battery cover after being run over by a car. However, had we not changed the mount countless times, the screw probably wouldn't have broken, and the battery cover is still sealed and secure.
During our research and tests, we came across a YouTube channel where the Holosun device was also meticulously and extensively tested, and we wanted to share this review with you:
https://www.youtube.com/watch?v=NDmGC0Wlyro
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