Why a Rifle Zeroed in at Close Range Is Also On-Target at Longer Range

View of trees through rifle sight
How to get your rifle sighted correctly. Berggren, Hans / Getty Images

A puzzle to beginning shooters is how a rifle with sites adjusted and zeroed in for a close distance, such as 25 yards, can also show good accuracy at a considerable distance out, perhaps more than 200 yards. More than one shooter had seen this phenomenon: a 30-06 sited in at 25 yards will hit a bit high out to 200 yards or so, and then hit the point of aim at a longer distance before dropping lower at longer range.

This may seem very odd at first until you understand the physics involved.

The Physics of Bullet Arc

It's important to understand that a bullet travels in an arc when it's fired. As soon as it leaves the muzzle of the gun, gravity starts to pull it downward. Guns are designed so that the bullet is actually fired upward at a very slight angle. As it travels away from the gun and gravity begins to exert its pull, the bullet's path becomes curved, with the concave side of the curve facing the Earth.

Obviously, though, your line of sight through a scope or using iron sights is a straight line. So the trick is to get this straight line of sight to intersect the curve of the bullet's path at the best point. 

For a deer hunter or big game hunter, your goal is to sight the rifle so that you can aim at the center of a "kill zone" (the vitals) at any range out as far as your rifle will effectively reach, and have your bullet hit within that zone.

If your normal expected shooting distance is 25 yards from your game, for example, then you will zero in your sights at this distance, so that you do not have to adjust for bullet drop.

Remember though, that your bullet is traveling in a concave arc, and at 25 yards or so, your gun is sighted to intersect the path of the bullet when it is still on its upward arc out of the gun.

What goes up must come down, though, and there will be another point, at a much greater distance, where the downward arc of the bullet will again intersect that straight line of sight. This explains why there is a point where a gun zeroed in at 25 yards will have another mysterious sweet spot when it is dead on target at a much further distance. At the shorter distance, your line of sight is catching the bullet on its upward arc, while at the longer distance, it is intersecting the bullet while on its downward arc. 

After you shoot the rifle at 25 yards and adjust the scope so the bullet hits right where you aim, you can move on out to 50 yards and then 100 yards (or farther) and see how you're doing, and make whatever adjustments are required at those ranges.

Deer Hunting Bullet Guide

For deer hunting, you want most rifles to hit in the center of the target horizontally (side-to-side), and about 1.5 inches above the center of the target vertically (up-and-down) at 100 yards. This usually gives you the capability of aiming at the center of a deer's vitals and hitting within that zone out to 200 yards or more.

This is sometimes called point-blank aim, and a gun's maximum point-blank range is the distance at which the bullet falls below the bottom edge of the imaginary cylindrical tube that illustrates the size of the vital zone of the game being hunted.