Zeroing a rifle scope without wasting a box of ammo

A badly mounted scope cannot be adjusted: it drifts. Before the first shot, check that the rings match the tube diameter, that the height lets the objective clear the barrel, and that you tighten to what the maker states.

Check alignment too: a scope forced into misaligned rings is under stress, and the tube can get marked. A clean mount shows in a scope that sits without force, its screws tightened in a cross pattern, little by little.

Turrets move the point of impact, not the reticle. On most scopes the turret marked “up” raises the impact and “right” moves it right. Some work the other way: one control shot after two clicks settles it.

The value of one click is marked on the turret or in the manual. It is given in minutes of angle (MOA) or milliradians. At 100 metres, one minute of angle is about 2.9 cm: that is the basis of every correction you will work out.

Set up in the position you will actually use, with a stable rest and a paper target whose centre you can see. Fire a first group of three to five rounds, always aiming at the same point, without trying to correct between shots.

Then measure the offset between the group centre and the aiming point, on both axes. Convert to clicks, apply the correction, then fire a control group. Two or three cycles are enough when the correction is calculated; ten shots by feel achieve nothing.

The zero distance depends on your use: the shorter it is, the sooner the trajectory drops beyond it; the longer it is, the more a close shot needs correcting. The hunting ground or the range usually imposes its own distance, and that is the one to take.

A group is judged on its centre and its spread, never on the round that happens to land in the right place. Three tight impacts 4 cm to the right tell you something precise; three impacts scattered around the centre mainly tell you the position is not stable.

If the spread is bad, adjusting the scope does nothing: you are moving a group you do not control yet. Go back to the rest, the breathing and the trigger finger, then start again. A clean group zeroes in five minutes; a scattered one takes all morning.

Think about parallax too: if it is adjustable and set wrong, your eye does not sit behind the reticle the same way from shot to shot, and the point of impact shifts with the scope blameless.

A setup is only confirmed by a control group fired with the same ammunition, the same position and the same rest. Once you have that group, photograph the turrets: the photo beats every marker-pen line, which rubs off.

After transport, after taking the scope off or after changing ammunition, repeat the check before using the gun in earnest. A lost zero is found at the range, not at the moment it matters.

Finally, store the scope with its cover on and refit the objective cap: optics dislike sand, knocks in the trunk and abrupt temperature swings.

Before blaming the optic, rule out the mechanical causes: loose rings, a poorly fixed rail, a dirty barrel, new ammunition with no fresh check. A point of impact that drifts gradually usually points to a mount under stress, not a faulty scope.

If the group opens up clearly and the mount is sound, have the gun and the scope checked by a professional. A scope that has taken a knock can keep a perfect image and no longer hold its settings: that is a fault you cannot see by eye.