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Boresight (firearm)
Boresight (firearm)
Boresight (firearm)
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Rifle bore sighter with arbor and leather case
A German Luftwaffe technician uses a collimator to boresight the gun firing through the propeller hub of a Messerschmitt Bf 109 (1941)
Boresighting the gun on an M1 Abrams tank (2005)

Boresighting is a method of visually pre-aligning a firearm barrel's bore axis with the target, in order to more easily zero the gunsight (optical or iron sights). The process is usually performed on a rifle, and can be accomplished either with the naked eye, or with a specialized device called a boresighter.[1]

Optical boresighting

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Optical boresighting, also referred to as "eyeball boresighting", as the name suggests, involves using the naked eye and the bore axis of a firearm to dial in the sights of a firearm. Based on the type of firearm the procedure for optical bore sighting will vary. For AR style rifles the upper receiver can be dropped from the lower receiver and the bolt carrier group (BCG) can be removed exposing a clear line of sight through the barrel. With the upper receiver fixed in place you can then co-witness through the barrel and the sights on the top of the rifle, while doing this you can visually align the bore axis with the sights on a desired target. For bolt actions rifles the process is the same aside from the ability to remove different receivers, but the bolt can still be removed to view through the barrel.

Once you are able to align the bore axis and the sights on the firearm you should then be able to at least get shots on or close to the target. With the rifle reassembled you should be able to put shots down range and make more fine-tuned adjustments.

A drawback of using the naked eye to boresight is that it can be difficult due to the tunnel vision and lack of brightness, especially with longer-barreled guns. A more advanced method of boresighting uses a collimator boresighter, an optical attachment similar to a scope sight, which fits onto the muzzle end of the barrel via a bore-diameter arbor and projects a grid pattern onto the sight picture.[2] Using this method, the normal sight (which is fixed to the receiver) and the collimator (which is fixed to the barrel) can be sighted to match. Most collimators have grid patterns for rechecking the zero after the barrel is sighted.

Laser boresighting

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A more modern method of boresighting is to use a laser pointer to illuminate the distant point of aim, rather than using visual inspection. This method is preferable because it has less parallax, allows more movement in the gun as the projected laser beam will stay true to the bore axis, and does not require removing the bolt.

As laser technology has become more affordable and portable, laser boresighters have become popular for sighting in riflescopes. One type of laser boresighter is shaped like a cartridge, and when inserted into the chamber projects a laser beam through the barrel onto the target. The user then adjusts the iron sights or scope reticle to align the point of aim with the projected laser dot. Another more commonly used type of laser boresighter is attached to the muzzle of the barrel, either inserted straight into the bore ("arbor" type) or held in alignment with the barrel via a magnet, and projects a laser beam onto the target. Again, the user aligns the sights to the laser dot on the target.

No matter which method of boresighting is used, the result is to align the sights to the spot where the barrel is pointing at a particular distance. Because of variations in the projectile trajectory and other factors, the boresighted rifle will always shoot below the boresighted spot and is only meant to approximate the actual points of impact, namely getting the shots "on paper" (landing in proximity to the point of aim). Live ammunition will need to be fired to further fine-tune the sighting process.

Accuracy is the measure of how well the sighted object is represented. It can be measured from a specific decision-making circumstance, like the orientation of notches of a gun barrel. Alternatively, the device could be designed to accommodate a range of circumstances and still be sufficiently accurate.

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Boresight (firearm)

View on Grokipedia
from Grokipedia
Boresighting is a method of adjustment in which an optical firearm sight or other aiming device is aligned with the 's barrel to ensure that the point of aim approximates the point of impact on a target. This preliminary process, typically performed without live , establishes a baseline for subsequent zeroing and enhances initial accuracy by matching the with the bore's axis. Common methods of boresighting include visual alignment, where the shooter looks down the barrel at a distant target and adjusts the sights to match; and laser boresighting, which uses a device inserted into the muzzle to project a beam onto a target at a set distance such as 10 or 25 meters for adjustment. These techniques are adaptable to various firearms, including rifles and machine guns like the M249, and often involve mounting aiming devices on rail systems before fine-tuning windage and elevation knobs. The process is essential for military and civilian applications, as it reduces ammunition expenditure during live-fire zeroing, minimizes errors from environmental factors like wind or distance, and ensures reliable performance in combat or hunting scenarios by confirming alignment across optics, , and laser pointers such as the AN/PEQ-15. Proper boresighting can achieve groupings within 4 inches at zeroing distances, serving as a foundational step for effective target engagement at ranges from 25 to 300 meters or more.

Overview

Definition and Purpose

Boresighting is a preliminary alignment process in firearms that visually or mechanically orients the of the barrel—the longitudinal centerline through which the travels—with the provided by the firearm's sighting system, including , optical scopes, or red dot sights. This method approximates the point of impact (POI) on a target without requiring live , using tools such as a borelight, device, or direct to establish rough parallelism between the bore and sights. According to U.S. Army Field Manual FM 3-22.9, boresighting involves aligning a visible or reference point within the barrel to a target, allowing adjustments to the sights for initial convergence. The primary purpose of boresighting is to minimize the initial angular deviation between the and the , serving as an efficient starting point for precise zeroing via live fire at the range. This reduces the number of rounds needed for final adjustments and helps ensure that early shots group closer to the aiming point, conserving and time. Misalignment exacerbates trajectory errors stemming from the inherent offset between the bore and sights—typically 1.5 to 2.5 inches for centerfire rifles—which causes the to follow an arched path under gravity before intersecting the at the designated range. At its core, boresighting addresses the fundamental discrepancy between the and : the defines the initial bullet direction, while the extends from the eye through the optic or to the target. Without alignment, the offset leads to vertical and horizontal shifts in POI, compounded by drop (due to ) and (lateral drift from crosswinds) over distance; boresighting compensates by pre-adjusting sights to bring these lines into approximate convergence at short ranges, such as 25 meters, facilitating accurate long-range performance. This mechanical principle is essential for reliable aiming, as even small misalignments can result in significant misses at extended distances. Boresighting finds primary application in , pistols, and shotguns, particularly during initial assembly, optic installation, or post-maintenance sight corrections, where it streamlines setup for hunters, sport shooters, and . For like the M16/M4 series, it supports integration with advanced and lasers, while for pistols and shotguns, it aids in aligning compact sighting systems to ensure consistent POI.

Historical Development

The practice of boresighting firearms, which involves aligning the with the sights for preliminary zeroing, emerged in the alongside the widespread adoption of rifled barrels and adjustable by hunters and military forces. Early methods relied on manual , where users peered down the open bore at a distant target to adjust sights accordingly, predating formal optical aids. This technique addressed the need for accurate alignment in an era when telescopic sights were rudimentary and expensive. In the early , boresighting gained formal recognition in military applications, particularly with the U.S. adoption of rifles like the during preparations. Army training emphasized visual bore alignment to ensure sight zeroing before live-fire exercises, reflecting its integration into standard rifle marksmanship doctrine. A significant advancement came in 1905 with George N. Saegmuller's patent for a bore-sight device, which used an apertured plate at the muzzle to project an image into the bore, allowing precise telescope alignment via cross-wires and adjustable mounts. This invention marked the transition from purely manual methods to basic optical tools, primarily for larger ordnance but adaptable to small arms. By the mid-20th century, optical boresighters proliferated in military contexts, especially during and after . In the 1940s, the U.S. Navy developed boresight telescopes, such as the Telescope Mk 8 Mod 6 and Mk 75 Mods 0 and 1, for aligning sights on anti-aircraft guns ranging from 20-mm to 3-inch calibers in aircraft and artillery systems. These collimating devices used lenses and reticles to simulate distant targets at short ranges, improving efficiency in naval gunnery maintenance. Post-war, these technologies were adapted for , with civilian commercialization of optical collimators beginning in the 1970s to support scope mounting on hunting rifles. The late 20th century introduced laser-based boresighting, revolutionizing the process for speed and precision. The U.S. Army patented the first laser alignment method in 1974 (filed 1973), employing a gallium aluminum arsenide laser diode in a breech-inserted canister to project a collimated beam observable through a viewing scope. Laser Products Corporation (now SureFire) commercialized the first firearm-mounted laser sight in 1979, patented earlier that decade, initially for tactical use. By the 1980s, dedicated laser boresighters entered the market, with patents like US5365669A (1994) describing cartridge-style devices for non-firing verification. Widespread adoption occurred in the 1990s as affordable consumer models became available, fueled by growth in precision shooting sports and integration with platforms like the AR-15 alongside red dot sights.

Boresighting Techniques

Traditional Visual Method

The traditional visual method of boresighting involves peering directly down the firearm's barrel to align the bore with a target, allowing subsequent adjustment of the sights without the need for specialized tools. This technique originated as a fundamental approach for initial sight alignment, particularly effective for bolt-action rifles where the action can be opened to provide unobstructed access to the bore. It relies on the shooter's eye to establish a parallel to the barrel axis, minimizing initial deviation during live-fire zeroing. To perform the procedure, first confirm the firearm is unloaded, with the chamber clear and safety engaged to ensure safety. Secure the rifle in a stable rest, such as a vise or sandbags, on a bench to eliminate movement and parallax errors. Remove the bolt (consult the firearm manual for model-specific instructions) and position the rifle so the bore points toward a well-lit target at 25 to 100 yards, centering the target's bullseye precisely in the bore's circular field of view. Without disturbing the rifle's position, shift focus to the sights or optic and adjust the windage and elevation turrets until the reticle or sight picture aligns with the same target center—typically moving the turrets in the opposite direction of the needed correction (e.g., if the reticle is left of center, adjust windage right). Replace the bolt, recheck the bore alignment, and repeat adjustments as necessary for confirmation, aiming for consistency across multiple views. This process typically gets impacts within a few inches at the initial zero distance, reducing ammunition expenditure at the range. Key requirements include a rigid, immovable setup to maintain bore-to-target alignment, an environment offering a clear, unobstructed (ideally outdoors with good lighting to enhance target visibility), and firearms with removable bolts or openable actions for optimal access—making it most practical for . Proper eye positioning is essential, with the eye placed directly behind the bore at a comfortable distance to avoid , ensuring a parallax-free view of the target. No tools beyond a basic rest are required, though a target with a distinct center, such as a 3- to 6-inch bullseye, aids precision. This method suits most centerfire but is less ideal for semi-automatics or those without easy bolt removal. Variations adapt the core technique to other firearm types. For pistols, visual boresighting is more challenging due to the slide's enclosed design, and or other tools are often preferred. Lever-action rifles follow a similar but may use shorter distances (e.g., 25 yards) due to limited bolt access, with adjustments made via the rear sight or optic after initial bore centering. These adaptations maintain the method's simplicity while accommodating design differences.

Optical Boresighting

Optical boresighting employs a , an optical device designed to be inserted into the firearm's barrel to simulate the and enable precise alignment of the sights. The collimator incorporates internal targets, such as crosshairs or bullseyes, visible through its integrated , which use reflective surfaces and lenses to replicate a distant target and simulate a view at optical . This setup eliminates errors and allows alignment without requiring an actual downrange target, making it suitable for indoor or controlled environments. The procedure begins with selecting a collimator matched to the firearm's caliber, for example, a .223 insert for an AR-15. The device is then secured into the muzzle or chamber, and the shooter views the internal target through the barrel end using the firearm's sights. Adjustments to the scope's windage and elevation turrets—or iron sights if applicable—are made to center the reticle on the collimator's target grid. After alignment, the device is removed, providing an initial zero that requires live-fire verification for final tuning. Collimators come in several types tailored to different firearms. Muzzle-mounted versions, secured by caliber-specific arbors or spuds, are standard for and longer barrels. For pistols, chamber inserts resembling dummy cartridges fit directly into the chamber to accommodate shorter barrels and enclosed actions. Adjustable models, often with interchangeable adapters, support various calibers and can account for differences in scope eye relief by allowing fine positioning within the bore. In terms of accuracy, optical boresighting typically achieves alignment within 3 inches at 100 yards, equivalent to about 3 , though results improve with stable mounting and controlled lighting to minimize shadows on the internal target. This method is versatile, compatible with scopes, red dot sights, and across and pistols, offering a repeatable alternative to direct visual peering for initial setup.

Laser Boresighting

Laser boresighting employs a compact, battery-powered device designed to fit into the firearm's muzzle or chamber, emitting a precisely aligned beam along the to facilitate sight alignment. The device, often shaped like a cartridge for chamber insertion or featuring a tapered arbor for muzzle mounting, ensures the laser beam simulates the bullet's path without requiring direct of the bore. Caliber-specific models, such as those for 9mm handguns or .308 rifles, provide a secure fit to maintain alignment accuracy. The alignment procedure requires securing the unloaded in a stable rest to prevent movement. The boresighter is inserted into the chamber or muzzle and activated, projecting the beam onto a target at 25 to 50 yards. Shooters then adjust the sights or optic's and to center on the dot, allowing verification at distance without repositioning the . variants enable use in low-light environments, projecting an invisible beam detectable via devices for tactical applications. Available types include cartridge-style boresighters that load directly into the chamber like , muzzle-inserted models with adjustable O-rings or cones for adaptation, and magnetic mounts that attach quickly to the barrel end for versatility across firearms. Red lasers suit general daylight use due to their cost-effectiveness and battery efficiency, while green lasers offer superior visibility in bright conditions, extending up to 100 yards at night. Some advanced models incorporate built-in levelers or adjustable cones to ensure proper scope reticle orientation during alignment. In terms of accuracy, laser boresighting typically gets shots on paper at 25 yards, providing a reliable starting point that minimizes live-fire adjustments, though results vary with device quality, beam , and lighting. At distances up to 50 yards, it effectively places shots on paper for most rifles and pistols, but longer ranges introduce limitations from and unaccounted ballistic factors like bullet drop. Final zeroing with live remains essential, and infrared models enhance precision in scenarios without compromising tactical stealth.

Practical Considerations

Advantages

Boresighting provides significant savings by establishing an initial alignment between the firearm's bore and sights, reducing the live rounds needed for final zeroing from potentially dozens to a more manageable few. In applications, for example, it ensures the first shot group strikes near the intended target during zeroing procedures, thereby minimizing wasteful firing due to gross misalignment. This efficiency is evident in contexts as well, where bore-sighting gets shots on paper at 25 or 50 yards, avoiding excessive rounds during sighting-in. The process also improves time efficiency, enabling quick initial setups in minutes at home, in a , or on-site, which shortens range sessions overall. This is particularly advantageous after installing a new scope or changing sights, allowing users to focus more on refinement than basic alignment during live-fire activities. Cost-effectiveness is another key benefit, as boresighting conserves expenses and reduces wear on the barrel and suppressor by preventing shots fired from incorrect alignments. In structured training, it streamlines zeroing to require fewer resources, lowering overall preparation costs. Furthermore, boresighting enhances safety and builds confidence by verifying basic functionality before live fire, which is valuable for beginners and in competitive settings to confirm mount stability. It fosters reliability assurance without immediate risk. Its versatility extends to diverse firearms and environments, including low-light conditions via methods, making it suitable for both and civilian use without specialized setups.

Limitations and Best Practices

While boresighting provides a preliminary alignment between the firearm's bore and sights, it is not a substitute for live-fire zeroing, as it fails to account for ballistic factors such as bullet drop, spin drift, and environmental influences like wind and . This limitation typically results in an alignment accurate to within 2-4 inches at 100 yards, rather than pinpoint precision. Potential issues from device misalignment—such as improper insertion of the boresighter—or errors in the optic can introduce further deviations. Boresighting is also less reliable for extreme ranges beyond 100 yards or suppressed firearms, where added weight alters barrel harmonics and shifts the point of impact without compensatory adjustments. Common errors that undermine boresighting include insecure firearm mounting, which allows subtle shifts during the process; selecting boresighting devices mismatched to the firearm's caliber, leading to poor fit and unreliable projection; and neglecting to level the scope or maintain proper eye relief, which exacerbates alignment inconsistencies. Best practices emphasize treating boresighting as an initial step only, followed by live-fire verification at the intended zero distance, such as 100 yards for most rifles. Secure the firearm in stable rests, like a vise or shooting bags, to minimize movement, and calibrate boresighting devices periodically by checking their alignment against a known reference. For pistols, which have shorter sight radii and demand closer tolerances, perform boresighting at reduced distances of 10-25 yards to enhance usability. Store devices in protective cases to prevent damage that could affect bore alignment. Boresighting is inadvisable for heavily customized firearms or those prone to significant barrel harmonics, where mechanical variations may render the process ineffective; in such cases, consult a professional for precise adjustments.

References

  1. https://www.misawa.af.mil/News/Photos/igphoto/2001684413/mediaid/1645452/
  2. https://rdl.train.army.mil/catalog-ws/view/100.ATSC/4BEFBB3D-7A12-4E22-97A6-50E841CF90C3-1495568587177/tc3_22x249.pdf
  3. https://www.marines.mil/Portals/1/MCRP%203-01A%20z.pdf
  4. https://www.globalsecurity.org/military/library/policy/army/fm/3-22-9/c08.htm
  5. https://www.accurateshooter.com/optics/determining-scope-height-above-bore/
  6. https://www.sightmark.com/blogs/news/boresighting-vs-zeroing
  7. https://www.sightmark.com/blogs/news/mastering-the-laser-boresight-a-practical-guide-for-new-shooters
  8. https://patents.google.com/patent/US803435A/en
  9. https://oaktrust.library.tamu.edu/bitstream/1969.1/166060/1/GUTIERREZ-THESIS-2017.pdf
  10. https://www.maritime.org/doc/boresight/index.php
  11. https://patents.google.com/patent/US3782832A/en
  12. https://www.surefire.com/surefire-story/
  13. https://patents.google.com/patent/US5365669A/en
  14. https://savagearms.com/blog/post/boresighting-your-rifle
  15. https://deerassociation.com/how-to-bore-sight-most-any-type-of-deer-rifle/
  16. https://www.fieldandstream.com/stories/guns/rifles/how-to-sight-in-your-hunting-rifle-the-right-way
  17. https://blog.primaryarms.com/guide/how-to-zero-a-pistol-red-dot/
  18. https://www.shootingtimes.com/editorial/optics_st_collimator_200904/100118
  19. https://tacticon.com/uncategorized/how-to-use-a-boresight-properly/
  20. https://patents.google.com/patent/US5787631A/en
  21. https://tacticon.com/shooting-skills/laser-boresight-essentials/
  22. https://1source.basspro.com/news-tips/shooting-gear/25105/laser-boresight-buyers-guide
  23. https://crateclub.com/blogs/loadout/how-do-laser-bore-sights-work-a-comprehensive-guide
  24. https://www.sightmark.com/blogs/news/sightmark-readyfire-ir6-stay-on-target-in-complete-darkness
  25. https://www.cvlife.com/blogs/news/why-green-laser-boresighter-is-better-than-red
  26. https://crateclub.com/blogs/loadout/how-accurate-is-laser-bore-sighting
  27. https://proarmory.com/blog/top-5-best-laser-bore-sights-of-2025-comprehensive-reviews/
  28. https://rdl.train.army.mil/catalog-ws/view/100.ATSC/A736EED1-595B-4049-B7B5-1E0261D8E478-1495566423695/tc3_22x50.pdf
  29. https://www.adfg.alaska.gov/static/home/library/pdfs/wildlife/booklets_books/hunt_alaska_2012.pdf
  30. https://www.agmglobalvision.com/How-to-Choose-and-Use-a-Boresight
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