The Basic Idea: A Foundation, Not a Guarantee
At its core, boresight zeroing is about creating a visual alignment between your rifle’s barrel and the scope’s crosshairs. This is typically achieved using a specialized tool, such as a laser boresighter, a collimator, or, in some cases, simply looking down the barrel to align with a distant object. The idea is to get your optic pointing in roughly the same direction as where your bullet is destined to travel. This allows the shooter to get “on paper” quickly, meaning the shots should at least land on the target, somewhere. From there, the final adjustment can be done.
The appeal is clear: it streamlines the initial setup. Instead of firing a series of shots, making adjustments, firing again, and repeating, boresight zeroing promises a quicker path to your first live rounds. It cuts down on wasted ammunition and range time, making the overall zeroing process seem faster.
However, the inherent nature of the tools and techniques used for boresighting means that accuracy, in the ultimate sense, is often a casualty of this speed. It’s crucial to understand that boresight zeroing provides a ballpark estimate, not a guarantee of pinpoint precision. It provides a foundation, but not the final, accurate product.
The Accumulation of Small Inaccuracies
One of the most significant reasons why boresight zeroing falters in the accuracy department revolves around the concept of tolerance stacking. Manufacturing tolerances are unavoidable in the production of both firearms and optics. Each component, from the barrel to the receiver, the scope mount, and the optic itself, has a degree of allowable variation. These tiny discrepancies, seemingly insignificant on their own, can combine and accumulate, leading to a noticeable shift in the point of impact at the distances we typically shoot.
Consider the barrel. It may not be perfectly aligned within the receiver. The receiver, in turn, might have slight imperfections. The scope mount, whether a set of rings or a Picatinny rail, can be off. And, of course, the optic itself is manufactured to within a tolerance. When these small variations are added together, they can easily result in a misalignment between the crosshairs and where the bullet actually hits.
A slight cant, for example, a small tilt of the rifle or scope during the boresighting process, can significantly affect the point of impact at longer distances. A seemingly minor deviation at the start of the bullet’s trajectory becomes amplified as the bullet travels downrange, causing the shot to stray from the intended point of aim. The farther you are shooting, the more exaggerated these effects become.
Tool-Related Challenges: The Weak Links in the Chain
The effectiveness of boresight zeroing is heavily dependent on the tool being used, and unfortunately, each type of tool comes with its own set of potential inaccuracies.
Laser boresighters
Laser boresighters, perhaps the most common type, project a laser beam down the bore of the rifle. While convenient, these tools can suffer from alignment issues. The laser might not be perfectly centered in the bore, or the tool itself might be slightly misaligned when inserted into the barrel. Furthermore, the accuracy of a laser boresighter can be influenced by the light conditions at the range. Bright sunlight can wash out the laser’s dot, making it difficult to see the point of impact on your target.
Collimators
Collimators present another set of challenges. These devices typically use a lens system to create a virtual target at infinity, allowing the shooter to align the scope’s crosshairs. Collimators rely heavily on the user’s ability to center the crosshairs precisely. This can be a subjective task, prone to parallax errors. Parallax, the apparent shift in the target’s position based on the viewing angle, can also introduce inaccuracies if the user isn’t properly positioned behind the optic. The collimator’s internal components, too, could be slightly off, further contributing to the potential for error.
Chambered Boresighters
For chambered boresighters, there are also possibilities of inaccuracy. These bore sighters are designed to fit within the chamber of the rifle. However, these types of bore sighters can also have issues with alignment, especially if they are not manufactured to very high tolerances.
Environmental Considerations: External Influences on Performance
Environmental factors can further erode the accuracy of boresight zeroing, especially when using a laser boresighter. Wind, for instance, can affect the laser beam’s direction, albeit minutely, leading to a slightly skewed alignment. Extreme temperatures can also potentially impact the laser’s performance, although this effect is usually minor. Furthermore, the way the firearm reacts to the temperature may have an effect. For instance, the temperature may affect the metal expansion which could affect accuracy.
The Human Factor: The Importance of Technique
Finally, the person using the boresighting tool plays a critical role in determining the accuracy of the process. Poor technique can easily negate any benefits the tool might offer.
Failing to properly center the boresighting tool within the bore or chamber, not properly leveling the rifle or optic, or not accounting for parallax can all contribute to significant inaccuracies. The shooter’s attention to detail and consistency of method are critical. The quality of the tool is only as good as the person operating it. Even a high-quality laser boresighter will be rendered ineffective if the user does not employ sound practices.
Superior Alternatives for Precise Zeroing
Because of these limitations, the most reliable way to achieve an accurate zero is through the use of live-fire zeroing. This method involves firing rounds at a target and making adjustments to the optic based on the bullet’s impact point.
Live-fire zeroing is the gold standard. It’s the only method that takes into account all the variables specific to the rifle, optic, and ammunition being used. It’s the method that accounts for all the little nuances that boresight zeroing overlooks.
Selecting a suitable target and range is the starting point. A target with clear aiming points and a consistent backdrop allows the shooter to accurately assess bullet impact. The choice of range depends on the intended use of the rifle and the ammunition being used.
The adjustment process itself involves carefully observing the bullet’s impact relative to the point of aim and making the necessary corrections to the optic’s adjustments (windage and elevation).
Different approaches to live-fire zeroing exist, but the core principle is the same: use the shots fired to give the user information that allows them to adjust the optic.
Best Practices and the Right Approach
If you are going to use a boresighting tool, choose one of reasonable quality. Avoid the absolute cheapest options, as they tend to have lower precision and potentially higher manufacturing tolerances. Research reviews, compare features, and consider the type of tool that best suits your needs and budget.
Use the tool correctly. Always ensure the rifle is securely supported and level. Follow the manufacturer’s instructions carefully. Pay attention to the alignment process. If using a laser boresighter, make sure the laser beam is clearly visible, and take your time to center the dot on the target.
Understand the relationship between target distance and your chosen zero distance. The distance you are zeroing at is critical. For example, a rifle that is zeroed at a certain distance will have its point of impact rise above and fall below the line of sight at different ranges.
Always Confirm with Live Fire
Regardless of the quality of the boresighting tool and the care you take, always, always, *always* confirm and refine your zero with live fire. The purpose of boresight zeroing is to get the shooter in the “ballpark” and on paper. The final adjustments should always be made using real ammunition and by observing the impact of the bullets on a target at a known distance. Boresighting is a shortcut to a destination, but to truly nail the shot requires a few real rounds.
Conclusion: Using the Right Tools and Techniques
In conclusion, the question of why boresight zeroing is not always accurate boils down to the inherent limitations of the method. Tolerance stacking, tool-specific issues, environmental influences, and the human factor can all contribute to inaccuracies, especially at longer distances. Boresight zeroing is a valuable tool for getting on paper quickly and getting you to the next step.
However, the only way to guarantee a reliable and accurate zero is to confirm and refine it with live-fire zeroing, firing rounds at a target and adjusting your optic based on the bullet’s impact. Understand the limitations, select quality tools, and, most importantly, always verify your zero with live fire. Practice, patience, and a methodical approach are the keys to achieving consistent accuracy on the range.
