It’s important for all shooters to learn that boresighting and zeroing in your weapon are not the same thing. Some 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.
What is zeroing?
Zeroing is a method of adjustment to the sights so that the point of aim is the point of impact.
Although you can manually sight the bore yourself, the more modern method is with a laser that either attaches to the muzzle or is inserted into the chamber. The laser will emit a strong enough beam to see up to 100 yards away so you can easily align the bore.
While boresighting 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 wind and gravity will affect the trajectory of a flying object. The goal of boresighting is to get on paper. The goal of zeroing is to make the correct adjustments to guarantee the bullet hits where you’re looking.
These 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.