It’s important for all shooters to learn that boresighting and zeroing are not the same thing. Some shooters learn the hard way and end up wasting time, money and ammo before they figure it out. But once you understand a little bit about external ballistics, not only will the difference become simple, but in the meantime, you can also become a better shooter.
What is boresighting?
Boresighting is a method of adjustment to a firearm sight to align the firearm barrel and sights (rifle scopes or iron sights). Although you can manually sight the bore yourself in an arduous process that involves removing the bolt (for bolt action rifles), the more modern sighting process is with a laser dot that either attaches to the muzzle or is inserted into the chamber.
The laser will emit a strong enough beam through the gun barrel to see up to 100 yards away so you can easily align the bore. The details and step-by-step instructions concerning laser boresights are also available here.
While laser bore sighting will get the scope aligned with the bore, it is not 100% aligned with the point of impact from a bullet, as outside factors such as movement in the gun, wind and gravity will affect the trajectory of a flying object.
What is zeroing?
Zeroing is a method of adjustment to the sights so that the point of aim is the point of impact.
The goal of zeroing is to make the correct adjustments to guarantee the bullet hits where you’re looking. You should have a spotter with a powerful spotting scope to help you in this process.
After boresighting, settle your reticle on the target and take a shot. Your spotter will tell you to adjust your windage and elevation turrets appropriately. You may be shooting low, high, too far left, too far right or…no call.
You should listen to your spotter and continue adjusting until you’re hitting bullseye.
Boresighting and zeroing are both essential steps before you start shooting seriously. Those who don’t boresight their weapon will go out to the field and waste round after round just trying to get on paper because their sights aren’t aligned.
Others believe the misconception that boresighting will automatically zero their gun, so they hit a bullseye at 25 yards but are then frustrated that they’re multiple inches off at 100 yards. This happens because they don’t take external ballistics into account.
External ballistics deals with factors affecting the behavior of a projectile in flight.
Once the bullet leaves the barrel, gravity will start to affect its vertical movement, and wind will affect the horizontal movement. The farther your bullet goes, the more it will drop.
This is why zeroing your weapon at 100 yards won’t zero it for 200 yards as well. Most firearm optics and sights come with adjustable knobs for elevation and windage for this very reason, and the MOA (Minute of Angle) measurement will tell you how much you need to adjust the scope at a certain yardage.