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. This ensures that your first shot will be on a large piece of target paper at a distance of about fifty yards. Boresighting not only gives you a reference point from which to actually start sighting in your gun, but saves time, ammunition expense, and occasionally your shoulder from recoil.
Bore sighting will NOT sight in your gun. This must be done by firing a specific type of ammunition at a certain distance.
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 it so it is pointing at the bullseye of a target about fifty yards away. 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 oldest way to boresight is with a collimator and arbors. Arbors are sometimes called spuds. 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 spuds must be sized accordingly, and although many collimating boresights come with several arbors, some calibers such as .17, or shotgun gauges require their own sizes and may not be available.
Another way to boresight, and the most convenient way, is to use a magnetic boresighter. These simply attach to your muzzle with strong magnets instead of inserting arbors into your barrel. Some people frown upon inserting anything into their barrels besides a cleaning rod. 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.
The third and final way to boresight is with laser boresighters. Some of these project a laser beam from an arbor or spud inserted into your muzzle, and some have the dimensions of a specific cartridge case that you simply insert into your gun's chamber and close the action. 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.
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 different kind of ammo will have a different point of impact.
- 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.