|Airsoft is an active movement sport. In the heat of mock-battle our replica BB-slingers undergo much abuse, often making contact with the ground or obstacles in our attempt to dodge the opposing teams BBs. We duck under chest-high brick walls, wait for a lull in the hostile storm of plastic, then, coming over the walls, slamming the bottom rail of our replica airsoft guns we center our aim through reflex sights, and pull our triggers. Our replicas jolt to life as either electric currents or expanding gasses flow to project a 6mm, round plastic pellet from our highly tuned devices, across the field and...
|...3 feet to the side of where our optics were pointed. What went wrong? We have a precision polished wide-bore barrel, a performance hop-up unit and rubber installed. We checked the air-seal and it's shooting at a good, consistent power, and the BBs are high quality and of decent weight. But somewhere along the line, a weak link in the chain of user, parts, and accessories has failed.
One of the first things that players often invest into after obtaining an airsoft replica is optics. These devices are designed to make aiming quicker, easier and more intuitive. However, many of the replica versions of these devices, specifically the cheaper ones, while attractive in value, are hit-and-miss (no pun intended) in quality and will as frequently cause you to miss as much as your shots are on target!
Now some airsoft players argue that zero-shift (the gradual shift of the optic's zeroing) is not so applicable to airsoft due to the low-to-no recoil of the replicas, but do their arguments hold any ground? We put this to the test.
The test would be conducted with two sights of two different designs and drastically different pricing, but both of them are red-dot replicas using the same or similar technology. Firstly we tested a no-name brand replica of an Aimpoint COMP-M2 and used its included cantilever mount. It costs us just under $20 and has been completely powder-coated in a tan color. As its opponent, we chose a Hurricane red-dot that has been designed to look like a 552 holosight. This mounts directly to the rail, uses AA batteries for convenience, and costs $190.
The test platform was a GHK G5. A GBB PDW known not only for its decent mid-range performance, but also for its very strong and incredibly sharp recoil. The sights would be mounted as far back as possible as to exert them to similar recoil.
Here is a video demonstrating the kind of recoil you get from the GHK G5 with Top Gas.
The actual test was simple. Using 0.3g BBs for accuracy, zero the sight, shoot a zeroed grouping at 10 meters, and fire 150 rounds (un-shouldered) through the G5 on full auto, then shoot a new grouping to see if the zero had shifted.
During the test, the no-name replica M2 red-dot sight already began to show problems as it could not be zeroed properly. The windage dial reached the end of its range of adjustability, having to be adjusted to the left the entire distance and still shooting right by about 1.5cm. Similarly, the elevation adjustment seemed to slip on the actual internal tube of the red-dot, making elevation zeroing difficult. Nonetheless, we continued with the test with a slightly off-zero sight.
After the 150 shots of full auto, a new grouping was fired. Lo and behold, the zero had shifted a full 5cm lower and slightly to the right. This confirmed that zero-shift was a real phenomenon and can occur. Given the high-recoil nature of the testing bed the number of shots required to cause the zero-shift would almost definitely be greater on other replicas.
By contrast, the Hurricane 552 style sight proved easier to zero with responsive windage adjustment, but the elevation was still a bit finicky to get to the correct position, on some turns of the dial, the reticule did not seem to move, while on other adjustments, the reticule jumped quite a bit. In the end, a zeroed grouping was almost dead on target.
The bad news is that the zero did appear to shift, even with the nearly $200 Hurricane replica 552. The good news is that it was only by less than 1cm to the left. This could be attributed to random chance or shooter error, but it did show a slight movement.
To conclude, the zero-shift phenomenon in cheap scopes does exist, but the test we conducted is not extensive enough to generalize across all cheap sights. It almost definitely is true that the quality control and durability of a $20 replica optic is not to be trusted, and several examples of the same model my, by chance, be of better build and durability (although the same is true for the opposite, they may be worse).
The improved design of the zeroing mechanism on the Hurricane 552 red-dot made for a tighter and more accurate grouping. In addition, the sight zero held almost perfectly over the 150 shot stress test, but while this definitely shows that it holds zero better, it doesn't necessarily indicate a complete immunity to zero-shift, as it is possible that a greater number of shots would produce similar results to the cheap red-dot.
As a final note, it is entirely up to the user to zero and re-zero his sight as often as is appropriate. Zero-shift can also occur during transport to-and-from war-game sites, due to impact against obstacles and movement and replacement of sights on an accessory rail. So even if you have a good optic, it is your responsibility to keep it zeroed and accurately on target.