Step 1: Set up a 25-yard target at the range.
Step 2: Remove the bolt, look down the rifle’s bore and center it on the 25-yard target. A 3- to 6-inch orange circle placed on your regular zeroing target helps make it more visible through the bore. The secret to success is to have the rifle in a rock-solid rest and to keep the bore centered on the target as you adjust the scope.
Left: A view of the 25-yard target through the rifle’s bore. Right: A view of the same target through the scope. The reticle is centered for windage (left to right) but the elevation is still too high.
If your scope reticle is left of the center of the target, adjust your windage knob to the left to move the reticle to the right. This process is the opposite of adjusting a bullet’s impact on the left of the target. Don’t worry about this detail because you will see the direction of the moving reticle as you adjust the scope. Since it is the opposite of how you normally adjust your scope, it feels odd the first time you do it. Adjust your elevation next. Your scope reticle now should be in the center of your orange circle.
Step 3: Your scope is now bore-sighted, and you are ready to fire your first shot at the 25-yard target. Remember, it takes four times the scope’s adjustment to move the bullet’s impact at 25 yards than it does at 100 yards. Thus, it takes sixteen 1/4-inch clicks to move the point of impact 1 inch at 25 yards.
Step 4: You want your bullet to impact 1-inch low from the center of the 25-yard target to be able to hit your target at 100 yards. Take a ruler to the range.
There are many factors that affect where a certain cartridge will impact at 25 yards with a 100-yard zero. There are ballistics programs that will give you the precise 25-yard impact. But the “1-inch low at 25 yards” rule of thumb will give you a 100-yard hit on your target almost every time with all types and calibers of center-fire rifle ammo. Then you can quickly proceed to finalizing your 100-yard zero.
1-inch low at 25 yards is the magic starting point for most deer rifles with scopes that are usually 1.75 to 2 inches above the bore. This measurement is taken from the center of the scope to the center of your rifle’s bore. For ARs and other rifles with scopes that are 2.5 inches or so above the bore, a 25-yard impact of 1.5 inches low will get you on target at 100 yards.
