Understanding the Basics of the 20 MOA Rail
The term “MOA” stands for Minute of Angle. MOA is a unit of angular measurement, and in the context of shooting, it represents the size of the group your bullets will impact at a certain distance. One MOA represents approximately one inch at 100 yards. Therefore, adjusting your scope by one MOA at 100 yards will move your point of impact approximately one inch. This understanding is crucial because it directly relates to how we compensate for bullet drop at varying ranges.
Now, let’s define what a 20 MOA rail actually *is*. A 20 MOA rail is a sloped mounting base for your scope. This slope, angled downward relative to the bore of the rifle, effectively “pre-loads” the scope with a certain amount of elevation. The purpose of this pre-cant is simple: to provide additional elevation adjustment to the scope without maxing out the internal adjustment travel.
Think of it like this: a standard, flat rail provides a neutral platform. A 20 MOA rail subtly angles the scope so that even with the elevation turret set to “0,” the scope is already aiming slightly upwards relative to the bore. This allows you to reach farther distances, as the bullet drops more and more. This is the advantage.
The Problem with Reduced Near Zero Capability
One of the most significant disadvantages of using a 20 MOA rail is the potential for a reduced ability to zero the rifle at shorter ranges. Because the scope is already canted upwards, the optical center is no longer aligned with the bore. This means that you might not be able to achieve a 100-yard zero without using a significant amount of internal elevation adjustment. In certain circumstances, with a scope that has a limited elevation range, it might not even be possible to zero at 100 yards at all.
Consider this example. You have a rifle set up with a 20 MOA rail, and your scope has 60 MOA of elevation adjustment. The rail is already eating up 20 MOA of that adjustment. If you intend to primarily shoot at shorter distances, like 100 yards, you will have used a significant amount of the scope’s internal adjustment to zero it at this range.
The implications of this are practical. If you are using the same rifle and scope setup for both shorter-range practice and long-range shooting, the 20 MOA rail can make it a challenge. For instance, you zero the rifle at 100 yards, and then switch to a 500-yard target. You’ll need to make significant elevation adjustments on the scope. The 20 MOA rail has taken away some of your scope’s adjustment travel, and in addition, it has made your zeroing process at shorter ranges more difficult. This will require careful calculation to get a solid zero at multiple distances.
Windage Limitations You Must Know
While the primary benefit of a 20 MOA rail is to extend the available elevation adjustment, a lesser-known consequence is the potential reduction in available windage adjustment. Scopes have a limited internal windage travel, and the 20 MOA rail can sometimes consume a portion of this, especially if the scope is not perfectly centered within the rings during installation.
Windage adjustment allows you to compensate for wind drift and to correct your bullet’s horizontal point of impact. If the 20 MOA rail causes the scope’s internal windage adjustment to be used up, it can limit the amount of wind correction you have available.
Imagine yourself at a long-range shooting competition. The wind is blowing strongly from the left. You need to make significant windage adjustments to account for the wind drift of your bullets. If the 20 MOA rail has already used up a portion of your windage travel, you might not have enough adjustment to make the necessary corrections.
This can lead to missed shots and a frustrating experience. The 20 MOA rail, designed for elevation, unintentionally impacts the ability to account for wind, a crucial element for long-range success.
Scope Quality and the 20 MOA Rail
The 20 MOA rail, while seemingly simple, has a direct relationship with the quality of the scope. The use of a 20 MOA rail increases the demands on the scope, meaning the scope’s internal adjustments need to be adequate, and its overall quality has to be high. If the scope does not have enough internal elevation travel, or if its internal components are of poor quality, the results can be disappointing.
One of the fundamental principles to consider here is the balance between the 20 MOA rail and your specific scope’s internal adjustments. When a 20 MOA rail is installed, the scope’s internal mechanisms are operating at or near their limit, especially when shooting at longer ranges. This extended use can accelerate wear and tear.
When you’re considering a 20 MOA rail, it’s crucial to ensure that the scope you are using is up to the task. Otherwise, it can result in diminished performance, less clarity in your sight picture, and a decrease in accuracy.
Optical Distortion and Its Impact
Beyond limitations in mechanical adjustment, the use of a 20 MOA rail can sometimes have subtle impacts on the optical performance of the scope. While modern scopes are designed with excellent optical quality, pushing a scope to its maximum adjustment ranges can introduce certain distortions.
When a scope is adjusted to extreme limits, optical aberrations can sometimes emerge, such as a less clear sight picture. These aberrations can be challenging to detect but can have a detrimental effect on your shooting performance.
The effects are subtle, but they can become important when shooting at extreme distances. These factors, when combined, can lead to a lower overall shooting accuracy.
Installation Challenges and Potential for Problems
Installing a 20 MOA rail isn’t always a simple process. It needs to be done with care. The correct installation is critical for ensuring that the rifle and scope are aligned properly. It also prevents unnecessary stress on the scope or on the firearm itself.
The installation process requires the use of proper tools and techniques. One of the critical steps involves using a level. A level helps ensure that the rail is mounted squarely on the receiver, minimizing the risk of any canting or misalignment. An improper mounting can interfere with accuracy.
Incorrect installation can also apply undue stress to the scope tube or its internal components, potentially leading to damage over time. Furthermore, if the scope rings are not aligned correctly, you could be forced to compensate with the scope’s internal adjustments, which will eat into your elevation and windage travel.
When a 20 MOA Rail Isn’t the Right Solution
While the 20 MOA rail certainly has its place in long-range shooting, it’s not the universally applicable solution. It’s important to recognize situations where a 20 MOA rail might be unnecessary or even counterproductive.
At shorter distances, bullet drop is less significant. In fact, for ranges from 100 to 300 yards, the bullet drop is usually manageable with the scope’s internal elevation adjustments, even with a standard, flat rail. At these shorter distances, the added elevation provided by the 20 MOA rail provides no advantage.
Another factor to consider is the available internal elevation travel of the scope itself. Many modern scopes have ample internal adjustment to handle typical long-range shooting scenarios. Therefore, a 20 MOA rail might be unnecessary.
Other Ways to Correct for Long-Range Shooting
It’s worth considering some of the alternatives to the 20 MOA rail, especially when seeking to optimize a long-range shooting setup.
Alternative rail options include the 0 MOA or 10 MOA rail. These options provide a smaller amount of pre-cant, which is suitable for certain rifles and scopes. This will avoid the need to adjust the scope so far in one direction that the scope’s optics are strained.
Adjustable scope rings also provide an alternative solution. Adjustable scope rings allow for slight adjustments in elevation to provide more correction, without the need for a canted base. This can be helpful in scenarios where a small amount of additional elevation is needed.
Variable base mounts offer another solution. These mounts allow you to adjust the elevation of the scope, providing greater versatility.
Conclusion
In conclusion, the 20 MOA rail is a tool with both advantages and disadvantages. It certainly provides extra elevation adjustment, allowing shooters to engage targets at extended distances. However, it is important to consider the limitations. Reduced near zero capabilities, and potential windage limitations must be considered. It is critical to match the rail with the scope.
Before investing in a 20 MOA rail, consider your typical shooting distances, the characteristics of your scope, and your overall long-range shooting goals. Carefully analyze the range of a rifle and scope set up.
Ultimately, the decision to use a 20 MOA rail is a personal one that requires careful consideration. Assess the factors that influence accuracy. This component may be the perfect solution for some, but it may be more detrimental to others.
