What a zero is, and what it is not
A zero is a distance at which your line of sight and the bullet's path cross. It is not a property of the scope, and it is not a setting the scope arrives with — the optic sits an inch and a half or more above the bore, pointing wherever the rings happen to aim it, and until you make them agree the reticle tells you nothing about where the bullet goes.
That has a consequence people find counterintuitive: a scope can be perfectly mounted, perfectly levelled and correctly torqued, and still be badly wrong. Mounting is a mechanical job; zeroing is an empirical one. You cannot compute your way to a zero, because it depends on your rifle, your load and your sight height together. You have to shoot it.
⚠️ Before you fire the first round, confirm the mount is genuinely finished — rings torqued in a cross pattern to spec, reticle levelled, eye relief set so you get a full sight picture from your natural shooting position. A zero built on a mount that later shifts is not a zero, and you will blame the wrong thing.
Boresighting — getting close before you spend ammunition
Boresighting aligns the bore and the reticle so your first live round lands somewhere on the target rather than somewhere in the berm. It is coarse adjustment; the range work is fine adjustment. Skipping it is what turns zeroing into an expensive scavenger hunt for a hole nobody can find.
On a bolt rifle you can do it with no tools at all. ⛔ Confirm the rifle is unloaded, then remove the bolt. Rest the rifle on bags or in a vise so it is genuinely steady and will not move — this is the whole trick, and a wobbling rifle makes the process worthless. Look through the bore from the rear and centre a distinct aiming mark, ideally around 25 yards, in the circle of the barrel. Now, without touching the rifle, look through the scope. The reticle will be pointing somewhere else. Dial the turrets until the reticle sits on the same mark the bore is centred on.
On a semi-auto, or anything you cannot see through, a laser boresighter does the same job — chamber or muzzle mounted, it projects a dot you can dial the reticle onto. Both methods get you close. ⛔ Neither is a zero: a boresight can be several inches off at 100 yards and still have done its job perfectly.
On paper at 25, then confirm at distance
Start close. A large target at 25 yards is very hard to miss even with a mediocre boresight, and being close compresses your error so the first group lands on paper where you can measure it. Use a big backer with a small, distinct aiming point — you want to be able to find the holes, and you want an unambiguous point of aim.
1. Fire a three-shot group from the steadiest position you can build. Not one shot — one shot tells you where one shot went, and you cannot distinguish a sight error from a shooter error with a single data point.
2. Measure from the centre of that group to your point of aim. Note both directions: how far up or down, how far left or right.
3. Adjust the turrets to move the group to the aim point, then fire another group to confirm the adjustment did what you asked.
4. Move to your intended zero distance and repeat. The 25-yard work only got you safely on paper; the real zero is confirmed at the distance you chose.
⚠️ Let the barrel cool between groups, and shoot from a position you can actually repeat. A zero established from a rolled-up jacket on a wobbling bench is a zero for that jacket.
Click math — turning a measured miss into turret clicks
Turrets move the impact in fixed angular increments, and the whole calculation is converting your measured miss into that unit. The two conventions are MOA and MIL. One MOA is very close to one inch at 100 yards, and scales linearly with distance — roughly half an inch at 50, two inches at 200. One MIL is 3.6 inches at 100 yards, and likewise scales.
Read your own turret; do not assume. A common MOA scope moves 1/4 MOA per click, so four clicks move one MOA. A common MIL scope moves 0.1 MIL per click, so ten clicks move one MIL. Both numbers are printed on the turret, and mixing them up is the single most common zeroing error.
The scaling is what catches people out at short range. At 25 yards, one MOA is only about a quarter of an inch — so a correction that would be four clicks at 100 yards takes roughly sixteen clicks at 25. Shooters who forget this dial a tiny correction, see almost no movement, and conclude the scope is broken.
🎯 Turrets are marked for the direction the impact moves, not the direction the reticle moves. If your group is low and left, you dial UP and RIGHT to bring the impact to the aim point. Say it aloud as you dial, because getting this backwards doubles your error and is very easy to do while concentrating on the arithmetic.
Choosing the zero distance
For a precision rifle, 100 yards is the near-universal default, and it is a good one: it is far enough that group size is meaningful, close enough to be available at almost any range, and it is the distance ballistic solvers and load data assume. Almost everything else in this curriculum is built on the assumption that you have a 100-yard zero.
There are reasons to choose otherwise. A 200-yard zero flattens the practical trajectory for field shooting, at the cost of the bullet running a little high at mid-range. Hunters sometimes reason in terms of maximum point-blank range — the furthest distance at which the bullet stays inside a defined vital zone with a dead-centre hold, which lets you ignore holdover entirely inside that band. The carbine's 50/200 zero, covered in its own lesson, is the same logic applied to a very different trajectory.
⚠️ Pick one and record it, because a zero you cannot state precisely is not usable data. Write the distance, the load and the date on the rifle's card. If you change ammunition, the zero is a claim about the old load until you confirm it with the new one.