Smoothbore muskets seldom even had a front sight, so the concept of zeroing used to be irrelevant.
Military guns of the 19th and 20th century had sights optimistically graduated, sometimes past a mile, but the only confirmed zero was usually armory-set point blank.
In most armies, guns were not individually adjusted to specific shooters until optical sights came into common use.
A History of Variables
With optics, several approaches exist. WW2 Japanese sniper scopes were pre-sighted at the factory and individually numbered to specific guns. How well did that work over time?
Not great, which is why typical engagement ranges were limited to 200 meters despite the relatively sophisticated bullet drop reticle indicating offsets out past a kilometer.
Most other scopes in use lacked bullet drop compensator (BDC) information but were individually adjustable. Some of the U.S. and German scopes used mounts permitting external range adjustment by tilting the entire tube.
With all those scopes, the default zero was 100 meters, with elevation changes made from that baseline. The same method was used with the more advanced post-WW2 BDC optics.
As the ranges of engagement rose for military snipers, longer zeroing distances became reasonable. Conversely, for police marksmen and hunters using scoped shotguns or pistol caliber carbines, shorter distances might make sense.
Let’s look at the determinants for the distance selection.
Determining Zero Distance
Point blank just means that a center hold would produce a hit on a target of a given size. Point blank on a torso of an enemy soldier maybe 275 yards, while on a prairie dog only 60 yards.
So the same rifle may be zeroed at 175 yards for a fight, but at 40 yards for a hunt. At the same time, this isn’t the only consideration for picking the zero distance.
If you have no expectation of encountering vary varmints up close, the zeroing distance should reflect the more realistic shooting environment.
So a 200-yard zero for the rodents just means your point-blank is 170 to 220, while shorter shots require holding under rather than over.
Similarly, if serious sniping is expected at 600 yards, it would make sense to zero that far and use a chart or a ballistic calculator to extrapolate shorter ranges. The error would be much smaller than with zeroing at a hundred and extrapolating to six.
The practical problem for most of us is the absence of ranges long enough to do that, and also the relative scarcity of actual long shots in either defense or hunting.
The Caliber Component
A quarter-mile shot is necessarily more deliberate than a snapshot across a yard, so more time is available for figuring out hold-overs at long range than hold-unders up close.
In most instances, the zeroing distance becomes mostly a function of the caliber:
- 50 yards or so for shotguns and PCCs
- 100 for slower rifle cartridges
- 200 for magnum or long-range rounds like .300 Win Mag or 6.5 Creedmoor
That simplifies the math of longer range adjustments, but we should keep in mind that elevation, humidity and temperature play a significant role in long-distance trajectories—verifying the calculated offsets on an actual target is the key to making accurate hits.
The simplest way to ascertain a hit would be to pick a piece of limestone (or some other reactive target) and try the exact ammunition in the hunting rifle at a location near the hunt.
If your 500-yard extrapolation is correct, you would get a hit, otherwise, your spotter would tell you if the shot went long or short, and by how much.