You see it every fall, at public and private shooting ranges across the country. Guys staple a target or two to a 100-yard backer, plop down at the bench and fire a couple shots. Then they squint through their scopes, retrieve their targets, pack up their guns and head home. "Yep, a couple inches high at 100--right where it was last year," they say. "I'm good out to 300 with this baby."

Properly zeroing a rifle for hunting is much, much more than that. And hunters who don't understand the principles and methods necessary to achieve a good zero are only cheating themselves.

Only when you've aligned its sight with the bullet's path can a rifle shoot where you aim it. The factory can roughly align iron sights, but the final zeroing is up to you. Factory technicians can't know which load you're going to use, or at what range you want to zero, and they may not look at the sights the way you do. When you mount a scope on the rifle, you'll have to zero from scratch.

Before you even touch the rifle, go to a loading manual. The ballistics charts found there show you the arc of your bullet so you can determine a useful zero range and proper holdover for longer shots.

Arc matters because your line of sight is straight, and it will contact the bullet's arc only in one or two places. It's possible to adjust the sight so it comes tangent to the bullet's arc, but a better tack is to thread the line of sight through the arc. Two intersections give you a zero range at the second crossing. Imagine a parabolic arc, the flight of a decelerating bullet that drops ever more steeply at long range. Now imagine a straight line angling into the arc from above and behind, but almost parallel to its starting path. The line will cut the arc, travel beneath it, then cut it again as the bullet plunges. That's your sightline. Between intersections, you want the sightline to stay close enough to the arc that you can ignore the gap.

If you're a target shooter, you must adjust your sight to zero for every yardage on the course. As a hunter, that's impractical because shots can come quickly and you'll seldom know the exact yardage. So before zeroing, you pick a maximum distance you'll allow the line of sight to dip below the bullet's arc. For big-game hunting, a reasonable maximum is three inches. If your bullet hits three inches above point of aim when you're shooting at a deer's chest, you'll still kill the deer. And of course, that much error occurs only at one distance--a little over halfway to the second intersection of your sightline and the bullet's arc.

By the same logic, you should be able to "hold center" on big-game animals to the range at which your bullet drops three inches below sightline. This is maximum point-blank range. You determine maximum point-blank range when you zero your rifle. Fast, flat-shooting bullets have a longer point-blank range than slow bullets that drop quickly, but the actual yardage is determined by your zero. Point-blank range also depends on how much gap you'll allow between trajectory and sightline at midrange.

So how do you figure the best zero range? Say you have a .30-06 and want to shoot 180-grain bullets at 2,700 fps. (Chronograph those factory loads; they commonly fall short of listed velocities.) And in this illustration, we'll use Nosler's reloading manual, where trajectory data for the 180-grain Partition bullet is based on a 200-yard zero.

Use your left hand to squeeze the rear bag under the stock, fine-tuning the hold.

At 100 yards, the bullet hits two inches above line of sight, and at 300 yards it's 8.5 inches low. The top of the arc comes a little beyond the 100-yard point (remember, the arc is parabolic), but still the bullet stays well within the three-inch maximum "lift" that we specified. So with this load, you could zero your rifle a bit beyond 200 yards, increasing maximum point-blank range. If you were willing to live with a 3.5-inch lift and drop, you could zero at 220 or 230 yards and stretch point-blank range to nearly 300.

According to the Barnes manual, a 180-grain X-Bullet stays within three vertical inches of line of sight to 300 yards--given the same zero and similar velocity.

Lower speed shortens zero range. Remington tables put 170-grain .30-30 Core-Lokt bullets about two inches high at midrange, given a 150-yard zero. So you could zero for greater range, though not much greater. A 200-yard zero lifts the bullet nearly five inches at its apex. A 170-yard zero is okay. You get a 200-yard point-blank range. That's far enough, given the bullet's punch and the iron sights common on .30-30 carbines.