What Causes Point of Impact Shift?

June 29th, 2024

Point of Impact (POI) shift refers to the deviation of a bullet's impact point from the intended point of aim. This phenomenon is inevitable due to various factors, including environmental conditions, rifle and ammunition characteristics, shooter technique, optics, etc. With advanced shooting techniques and high-quality gear, shooters can limit the point of impact (POI) shift to within an acceptable range, ensuring precise shooting.

In close-range shooting within 100 meters, POI shift usually is negligible. However, in long-range shooting, POI shift increases with distance changing. For instance, if the maximum POI shift is 1 cm at 100 meters, it will proportionally expand with increased distance. At 1000m, the maximum POI shift can increase to 10 cm, and at 500m, it can increase to 5 cm. This illustrates that distance amplify POI shift. These numbers are simplified for easy undetstanding. In real situation, the POI shift may vary.

For Vector Optics' Top line, Continental, the maximum POI shift is controled under 1/2MOA (around 0.5 inch) within 100 yard. That means, within 200 yard, the maximum POI shift would be 1MOA(1.047 inch), within 300 yard, the maximum POI shift would be 1.5MOA. VE continental line product, check the link here, PRODUCT-Rifle Scope & Red Dot Sight Supplier- Vector Optics.

POI can be mitigated but not avoided. In the following paragraphs, I am going to explain several points that would impact the POI shift.

The Inner Lens Movement after Recoil

Due to potentailly unreliable lens positioning in the design or assembly of the scope, internal lenses may shift under impact, causing a shift in the Point of Impact (POI). This means that even a slight movement of the internal lenses can cause the scope to lose its accuracy. Therefore, the quality of the scope's structural design and meticulous control of the assembly process are crucial to ensuring that the lenses remain securely in place and that the scope maintains its precision and reliability over time.

Magnification and Side Focus Adjustment

Magnification can cause a slight POI shift due to the movement of internal lenses within the scope. The quality of the scope's internal lens design determines its ability to maintain a consistent optical path.

When changing the magnification, the internal lens move according to its designed rail. Theoratically, the center of the image should stay consistent during the process. While the movement causes the axis deviate from being flat, leading to an optical path changing and further the POI shifting. As a result, the point of impact shift may increase along with the movement. Magnification allows the shooter to view the target with more detail, but does not directly cause the POI shift to increase.

Similarly, adjusting the side focus for parallax setting leads the inner lenses move to align with the desired focal plane. This movement can also cause the POI shift as the optical axis deviates.

Magnification range

Scopes with a wide magnification range, for instance, 6x, 8x, or even higher, require complex internal lens design. Adjusting magnification causes relatively significant lens movement compare to that of low magnification range, leading to greater POI shift. As a result, high magnification scopes often present substantial POI shifts due to the lack of delicate internal lens design.

Mount Setting

The movement of a rifle mount directly affects the scope's position, leading to shifts in the Point of Impact (POI). The quality of the mount is crucial, with three main factors determining its stability: material durability, torque application, and slot precision.

During shooting, recoil can cause significant movement if the mount is not secure, resulting in POI shifts. Therefore, the stability of the mount is essential for consistent accuracy.

Two primary factors influence mount stability: the quality of the mount and its proper installation. A high-quality mount ensures precise slot dimensions and durable materials, providing the necessary stability to minimize POI shifts.

Proper torque application is also critical. Too big or uneven torque can cause the scope to sit improperly on the mount or lead the scope's inner system distort, leading to POI shifts. And with the recoil, the POI shift may be more and more serious.

In sum, ensuring a stable, high-quality mount with precise torque application is vital for maintaining consistent and reliable performance of point of impact.

POI shift always exits

Shooters cannot completely eliminate POI (Point of Impact) shift, as it is influenced by numerous factors, including the firearm itself, the shooter's technique, and environmental conditions, etc.

Concerning bullet ballistics, bullet weight, shape and velocity influence trajectory, which further leads POI shift. A high-quality or expensive bullet possesses smaller POI shifts compared to that of cheap bullet.

Different firearms exhibit varying recoil patterns, leading to diverse POI shifts. Even with the same gun, ammunition, and shooter, perfect consistency is unattainable due to inherent recoil dynamics.

Scopes and firearms made from different materials expand or contract unevenly with temperature changes, causing POI (Point of Impact) shifts. Therefore, when shooting in changing weather conditions, even if you have adjusted the side focus and parallax settings for precision, material expansion or contraction would result in serious POI shifts. Temperature fluctuations affect materials differently. Metals and composites used in firearms and scopes expand at different rates, potentially leading to misalignment. For example, an aluminum scope mount may expand more than a steel rifle barrel, causing the scope to shift slightly and altering the POI.

Additionally, frequently changing or re-mounting scopes can lead to variations in mount settings, causing significant POI shifts even when reverting to the original setup.

Multiple factors contribute to POI shift, making it a persistent challenge for shooters to achieve precise accuracy. Usually people apply high-quality scope with delicate inner lens design to mitigate the POI shift. To improve shooting precision, understanding and mitigating these factors through proper equipment maintenance, consistent technique, and environmental compensation are essential.

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