Tips to Finding the Right Zero
November 17, 2016
These days, "long-range" shooting — whatever that means — is all the rage. We could discuss at length the ethics of taking shots at game at extreme distances and also how real what you see on TV may actually be.
Instead, let's be honest: In the East, I'm willing to bet that the average shot at a whitetail still lies inside 100 yards, and in the West, on game including mule deer, elk, pronghorn and the rest, I'll wager the average shot lies within 200 yards.
Most campfire arguments center on being undergunned, overgunned or making exactly the right choice. Fun stuff, but it's silly because there are a lot of right answers.
The argument we don't hear much is the proper sight-in: Is your zero too high, too low or just right? As we sally forth with the steadfast belief that a quarter-mile shot will be minimal (and the childlike faith that half-mile shots are practical under field conditions), I think all too many of us establish a sight-in that is too high at 100 yards and thus are zeroed at too great a range.
For instance, it is very common today to zero for 300 yards. With a few exceptionally flat-shooting cartridges, you can get away with this. Examples are the .257 Weatherby Magnum, .26 Nosler and .270 Winchester Short Magnum.
For instance, with a 140-grain bullet at a screaming 3,375 feet-per-second, you could sight the .26 Nosler 2.6 inches high at 100 yards, be 3.2 inches high at 200 yards and be dead-on at 300 yards. But there aren't many cartridges that shoot that flat.
More typically, to achieve a 300-yard zero, you must sight-in at least 3 inches high at 100 yards. That in itself isn't a problem, but 100 yards is not the height of the trajectory curve. The bullet keeps rising above line of sight until it reaches what we call midrange trajectory — generally somewhere just past 200 yards — then the curve starts back down to deliver the bullet at line of sight at 300 yards.
With most cartridges, that maximum midrange height of trajectory will be at least 5 inches and sometimes more than 6 inches above the line of sight. Theoretically, that should not cause a miss on a big-game animal, but I guarantee you it will sooner or later.
Here's why: Unless we grossly underestimate the range, it's unusual to hit low. It's a lot more common to both aim too high and hit too high. There are reasons. We often don't trust our instruments. Despite all the talk about 800-yard shots, game animals look pretty small at 250 yards.
So, it's normal to mistrust the range and hold a tad high "just in case." Also, our view of an animal is often distorted. If it's standing in grass or low brush, which is common, we may see only the top horizontal half, so we're already aiming higher than we should.
In other words, I don't buy the old biz about "sighting in for maximum point-blank range," often formalized as Max PBR. The goal in Max PBR is to sight in as if you were shooting down a pipe, the diameter of which you can set (8 to 10 inches is common for big game).
The bullet can't rise above the upper limit of the pipe, and when it drops out the bottom of the pipe, that's your Max PBR; just hold center and shoot. I don't like it because my own most common aiming error is to shade a bit high, as it is with most folks.
The higher the midrange trajectory height, the more likely I am to shoot over the top of an animal at medium range. So, what about long range? Well, to me that doesn't matter. Not because I can't or won't shoot at distance but because trajectory is, after all, just a set of numbers. At some point, you will have to hold over your desired point of impact, and at that point you must know your trajectory exactly and precisely.
You could, of course, simply zero at 100 yards and then know your holdovers for all ranges beyond, but that seems too limiting for modern flat-shooting cartridges. Maybe, as in so many things, Jack O'Connor was right all along. He always suggested a simple zero of "a couple inches high at 100 yards" so as to be dead-on at 200 yards or perhaps a bit farther.
Beyond that, you'll have to know your trajectory and consciously adjust, but, understanding the difference between real ranges and TV ranges, at 300 yards and beyond you must know your trajectory.
I have gone full circle. I've tried 300-yard sight-ins, and with the exception of a small handful of very fast cartridges, a 300-yard zero creates too much trajectory rise for me. Today, I'm back in Professor O'Connor's class.
Typically, with either a dial-up turret or a range-compensating reticle, a 200-yard zero usually validates the data anyway. With a very flat-shooting cartridge, whether a .270 Winchester or .300 Magnum, that isn't much more than 1 inch high at 100 yards and is rarely more than 2 inches high. Even with my propensity to shoot high, I can't get into too much trouble.
At 250 yards, I have to consciously hold toward the top of the shoulder, and at 300 yards I can dial the range, use a stadia line or simply hold just below the backline. It isn't complicated.
It can become complicated, however, when things change suddenly. When I took my last wild sheep, I got my gun case from the airline, but I didn't get my duffel bag with my ammo.
I was zeroed at 200 yards with a fast 165-grain load in my Blaser's .300 Weatherby Magnum barrel, and that was the zero that validated my stadia lines. The only ammo available were 190-grainers — a big difference — and there wasn't enough of it to do a lot of shooting.
Clearly, my stadia lines and all my data were useless, so I took notes from Professor O'Connor and left it about 2 inches high at 100 yards, expecting I'd be dead-on at about 225 and would need to adjust from there.
The shot was actually 253 yards, and I expected a bit of drop. Wow, that load was flatter than I thought. I held high on the shoulder, and the bullet hit exactly where I aimed. The ram went nowhere, but I wasn't far from shooting right over the top, and that's the classic error that I guard against when I sight in.