Boresighting is the process of aligning the bore (center of the barrel) of a gun with the sights on your firearm. It’s a relatively simple process and one that all shooters, including new shooters, need to learn. It also takes just a few minutes to boresight a firearm properly.
Boresighting aligns the optical sight on top of the gun barrel with the axis of your bore, and should be the first priority after mounting your scope. Boresighting not only gives you a reference point from which to actually start sighting in your gun, but saves time as well as ammunition expenses.
Bore sighting will not completely sight in your gun, this is the first step of the process to ensure you are on paper, and able to make minor adjustments depending on ammunition, overall distance and environmental conditions.
Origins of "Bore Sighting"
Boresighting is done by several different methods. The oldest way is to remove the bolt on a bolt action rifle and look down the bore. Secure the gun so it does not move, and position the firearm so it is pointing at the bullseye of a target . Now look through the scope, and without moving the gun, carefully adjust the elevation and windage turrets until the reticle is centered on the bullseye. Simple at that. You are sighted through the bore, or "bore" "sighted." Of course, this is not possible with many guns such as semi-autos, pumps, lever guns, and most handguns.
Collimators and Arbors
The next advancement in boresighting was to use a collimator and arbors. A collimator is a device with a graph-paper-like grid in it that is seen when looking through your scope. It is held in place by arbors inserted into your barrel from the muzzle end. They are sized for your caliber, and held in place by a spring or an expanding plug. The user then looks through his scope and adjusts the windage and elevation turrets so the crosshair is centered on the grid you see. The arbors must be sized accordingly, and although many collimating boresights come with several arbors, some calibers might not be available in the general package of arbors.
The newest form of boresighting utilizes in-chamber laser boresighters. These are more often aluminum or brass devices that look identical to shell casings per caliber. These are caliber specific, and instead of having powder inside the casing, they have a laser diode. Laser bore sighters do require a somewhat reflective target set some distance away to reflect your laser beam, and a steady hold or a gun vice to more easily center the scope's crosshairs onto the laser's dot. Most of these in-chamber do come with a red laser diode which is visible in sunlight at maximum 25 yds. These are a great and relatively inexpensive method for boresighting your firearms. The one nock is that it will require an added boresight purchase for every varying caliber that you have. For individuals with an AR, bolt-action deer rifle and another gun without an optic, this is not a significant investment, however for individuals that have many different calibers with optics, this could be rather taxing.
These magnetic boresights offer a slightly different variation to the in-chamber laser boresights. These simply attach to your muzzle with strong magnets instead of inserting arbors into your barrel. Magnetic bore sighters fit all calibers and gauges, and no other parts are required that can get lost or damaged. Magnetic boresighters can also be used to check zero after transporting your guns, or after a drop or hard use. To do this, sight in you gun and see where your crosshairs end up on your boresighter's grid. Remember the placement or write it down to check zero any time. These magnetic boresights offer a red or green laser diode allowing boresighting to occur at 25 yds (red) or 100 yds (green) during the day. Please keep in mind that when shining a laser down range, the size of the laser is typically much larger on paper. This is possibly the best device needed for individuals that own multiple calibers with optics that they would like to boresight.
Points to Remember about Boresighters
No boresighter will sight in a gun. This can only be done by shooting the gun with a specific type of ammo at a certain distance. Every kind of ammo will have a different point of impact, as well altitude, wind, and other environmental conditions. Remember to remove your boresight arbor before shooting. Simple enough, but I've seen some perfectly good barrels blown apart like a peeled banana by people who should've known better. Boresighting alerts you immediately to problems with mounting and scope adjustments and saves time, ammunition expense, and often physical abuse from recoil. Every shooter should own a boresighter whether he mounts his own scopes or not. As mentioned, these can be utilized as training aides in dry firing to determine if grip, trigger pull, or jerking is impacting shooters technique. Can be used for rechecking zero on a rifle once flying or setting up for a hunt or mission. The evolution of the boresight and techniques has provided several added advantages to the modern-day shooter.