Zeroing-In for Predators

Small animals call for bullet paths that stay near sight-line at mid-range, not arcs that cross it far away.

Zeroing-In for Predators

This CZ 527 hits just an inch high at 100 yards – a good zero, given the small animals targeted by .17s.

“It’s dead on.” When you ask someone if his or her rifle is zeroed and draw that reply, you might roll your eyes. I do. “Dead on” means the bullet lands where you aim, on the sight line. That can happen no more than twice during a bullet’s flight.

“Dead on at what distance?” you ask, cynically.

A bullet’s path is never truly flat. Unsupported after leaving the rifle, it starts to fall in a parabolic arc at the accelerating rate of 32.17 fps. Line of sight, on the other hand, is straight as a beam of light. A sight line parallel to the rifle’s bore would never cross the bullet’s descending route. Beginning at the muzzle, the gap between the bullet’s path and bore line just gets wider.

Zeroing or sighting-in, you adjust the sight line at a downward angle to the bore, so it meets the bullet’s path at least once. More commonly, and usefully, you zero so the sight line crosses it. From that point the sight line and bullet path diverge until gravity bends the bullet’s arc so steeply it intersects the sight line again. For most hunting rifles, that second and always final crossing is your zero range.             

The best zero range depends on your load and the shooting you intend to do. How far the bullet strays vertically at other distances depends mainly on its starting speed and its ballistic coefficient (BC). Scope height matters, too, because it changes the angle of sight line to bullet path.

You’ll want a 75-yard zero for rimfires on crow-size targets, so bullets don’t miss high at mid-range.
You’ll want a 75-yard zero for rimfires on crow-size targets, so bullets don’t miss high at mid-range.

Zero for Long Range

At first blush, the most practical zero distance seems to be that at which you expect to shoot most often. Verily, a longer zero is usually best. Here’s why.

When calling coyotes, you plan for a very close shot; but a call-shy animal or a turn in the wind can add many yards. If you miss or a second coyote rockets off when you drop the first, you might not have the rifle on target again or get clear aim until that animal tops a distant ridge.

Say you’re shooting a .243 Win. or a 6mm Rem. launching a 75-grain Hornady V-Max at 3,300 fps. Zero at 100 yards and your bullet will strike within 2.5 vertical inches of sight line from a few feet out to 200 yards. On the other hand, if you zero at 200 yards, that bullet will hit within 2.5 inches to 250 yards! No need now to adjust your hold until the animal is farther off. Just paste that crosswire where you want the bullet to hit. The chest of a coyote is big enough to catch bullets 2.5 inches high or low. Flat-shooting loads such as the .243s keep mid-range gap closer to 2 inches and extend practical reach a bit beyond 250 yards.

Short zeros waste the flat trajectories of sleek, fast-stepping bullets. But what if instead of a .243 Win. and its Mach 3 load you have Grandpa’s Savage 23C in .32-20 Win. with 100-grain XTP HPs at 1,300 fps? A 100-yard zero then makes more sense. You’ll hit about 2.5 inches high at 50 yards, and about that low at 130 yards. Zero a .32-20 Win. with this load at 150 yards and the mid-range gap grows to 7 inches.


Do the Math 

The chart here (with data from Hornady’s Handbook, 5th Edition, Vol. 2) shows how far bullets strike, in inches, above or below sight line at ranges from 50 to 300 yards, with zeros of 50, 100 and 200 yards. You’ll get similar results with bullets of like speeds and ballistic coefficients. For example, .25-06 Rem. figures apply as well to 150-grain 30-caliber boat-tail soft points at 3,200 fps. For predator loads at about that speed, a 200-yard zero delivers hits within 2.5 vertical inches of point of aim across a range of bullet weights and diameters — 55-grain .223 Rem. to 139-grain 7mm. Round-nose bullets throttled to 2,700 fps or so (.22 Hornet, .25-20 Win., .30-30 Win.) don’t meet that standard.

For any game, the most practical zero range is the farthest you can hit vitals without having to aim low.
For any game, the most practical zero range is the farthest you can hit vitals without having to aim low.

Velocity Vs. BC

Bullet velocity affects drop within practical zero ranges much more dramatically than does ballistic coefficient (BC), which takes over farther out. The 500 fps difference in speed between the .22 Hornet bullet and the 55-grain V-Max fired from a .223 Rem. is largely responsible for the 9-inch difference in drop at 300 yards (100-yard zero). After all, difference in BC is only .05. The 55-grain .223 bullet and the 100-grain .25-06 Rem. show double that disparity in BC, but exit speed is the same. The .223 bullet lands just 1.5 inches lower at 300 yards.

Even a small change in speed can move bullet impact, as shown by the 1-inch shift at 300 yards when 60-grain .223s are reined in just 100 fps. A 200-yard zero works for the .22 Hornet load only if you’re OK with a mid-range gap between sight line and bullet of nearly 3 inches. Better: a 150-yard zero — which is clearly the best option for the .30-30 Win. The .25-20 Win. begs a 100-yard zero.


Zeroing Too Long    

Excepting saddle guns still popular on lion hunts, most predator rifles these days are bolt actions that wouldn’t be caught dead in the company of .25-20s. Long zeros have become chic, as powerful optics and fast-twist barrels direct rocket-shaped bullets to steel plates dancing in mirage many leagues hence.

The temptation these days is to zero too long. Say you’ve got a new rifle in 6mm Creedmoor. It nips itty-bitty knots at 100 yards with 105-grain A-Max and 103-grain ELD-X bullets (G1 BC .500 and .512). So, you try it at 600 yards. Yippee! Softball-size groups! So why not zero to kill coyotes at 600?

Because the math says you’ll overshoot coyotes as close as 75 yards and as far as 550 yards. Sent at 3,000 fps from the 6mm Creedmoor (or a .243 Win. or 6mm Rem.) those missiles will fly 12.2 inches above sight line at 100 yards, 21.5 inches high at 200 and 25.7 inches high at 300 yards.

Well, that’s extreme. What about zeroing at 250 or 300 yards? A few flat-shooting rounds merit a 250-yard zero. Stretching to 300 yards, you incur a 4-inch mid-range gap, shown for the chart’s friskiest loads, the 87-grain .243 Win. and 139-grain 7mm Mag.

For any game, the most useful zero range is the farthest you can hit vitals without having to aim low. Most shots will happen within this point-blank range. You can take them quickly, without thinking. For the occasional poke at extreme range, you’ll likely have time to steady the rifle, gauge bullet drop and wind drift, shade where you must and make a careful, calculated shot.

Target size can also affect your zero. The 5-inch window (2.5 inches high and low) of a 200-yard zero is too tall for sure hits on prairie dogs with center aim at all ranges to 250 yards. You’d have to aim low at mid-range and high at 250 yards. To shrink that window, shorten the zero. Africa’s biggest predator, the crocodile, requires the same precision. An instant kill is the key to retrieving this mighty amphibious beast. To hit its tennis-ball brain at “the back of the smile,” zero for the distance from your blind to the bait.

Most big game is more forgiving. Hit within 2.5 inches of point of aim on a bull elk that tapes 28 inches back to brisket and your hunt is over.

I can’t blame a 200-yard zero on even one of the many shots I’ve bungled afield.                   


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