Air Rifle Accuracy
What Your Group Shape Is Telling You
Group size tells you how well you shot. Group shape tells you why. A 30 mm group that strings straight up and down and a 30 mm group that sits in a fat round blob measure identically and mean completely different things — one is usually a velocity problem, the other usually a pellet problem. Learning to read the pattern is the fastest way to stop guessing at fixes.
Most shooters only read half the target
The habit is to measure the group, note the number, and move on. That number is worth having — it is how you compare pellets and track progress, and there is a benchmark chart for what counts as good at each distance. But a single number throws away most of what the target is telling you.
Every group has an orientation, a spread and an outlier structure. Those three things narrow the cause down enormously. Below are the patterns you will actually see on paper, what each one usually indicates, and how to confirm it rather than guess.
Before you diagnose anything: shoot enough shots. Three shots can fall into almost any shape by chance. Five is a workable minimum, ten is meaningfully better. If you are reading a mechanical cause into a 3-shot group, you are reading noise.
The six patterns
1. Vertical stringing
Tall and narrow. Elevation is wandering; windage is fine.
This is the classic velocity signature. If the pellets are leaving the muzzle at meaningfully different speeds, they arrive at different heights — and the faster the string drifts, the taller the group. On a PCP the usual culprits are the fill pressure walking outside its sweet spot across the string, a regulator that is settling or creeping, or the air temperature changing while you shoot. On a springer, inconsistent hold and follow-through will do the same thing.
How to confirm: put the rifle over a chronograph and look at extreme spread. If ES is wide, the cause sits upstream of your aim. Note that pellet weight and fit affect ES in their own right, so a different pellet can be part of the answer rather than a distraction from it. Our guide to chronograph numbers covers what ES and SD figures are worth worrying about.
2. Horizontal stringing
Wide and flat. Something is pushing the pellet sideways.
Wind is the first suspect, and outdoors it is usually the answer. The tell is progression: if the shots walk steadily in one direction rather than scattering either side, a breeze was building while you shot. If conditions were genuinely still, look at yourself instead — rifle cant that varies shot to shot rolls the point of impact sideways, and so does inconsistent cheek and shoulder pressure.
How to confirm: shoot the same string in dead-calm conditions, or indoors if you can. If the width collapses, it was wind. If it doesn't, it's technique. Reading the wind goes into how much drift to expect from a given value.
3. Round but wide
No direction to it — just bigger than it should be.
Even dispersion in every axis means nothing systematic is pushing the pellet in one direction — the random error is simply large. Round is the default shape a group takes, so the question is what is making this one wider than it should be. Pellet fit and quality are the usual suspects: head size that varies across the tin, damaged or out-of-round skirts, or a pellet whose weight and shape your barrel doesn't like. Barrel fouling and a loose or shifting mount do it too — as, honestly, do you and your rest. And every rifle has a level of inherent dispersion below which it will not go.
How to confirm: run a proper pellet test — several candidates, same session, same conditions, everything else held constant. The best pellet guide sets out the method. If a different pellet tightens it up, you have your answer.
4. A tight group with one flier
The rifle is capable. Something interrupted one shot.
A single outlier well away from an otherwise tight cluster usually isn't the rifle. The common causes are a damaged pellet that went in with a dinged skirt, a shot pulled by a snatched trigger or a lost follow-through, or a pellet from a different tin or lot that got mixed in. Do rule out a moderator baffle being clipped, though — that one is the rifle, and it will keep happening. Bear in mind too that in a five-shot group the widest shot always looks isolated; one outlier is not automatically a flier.
How to confirm: the discipline that actually settles this is logging. Record the lot number of the tin you are shooting and call your bad shots as you release them. Over a few sessions the pattern becomes obvious — either fliers cluster around one lot, or they cluster around your own called shots.
A word on discarding fliers: only set aside a shot you can explain. Quietly dropping the ones you can't account for makes your groups look better than your shooting is, and it corrupts every pellet comparison you make afterwards.
5. Two distinct clusters
Two tight groups, not one loose one. Something changed mid-string.
This is the most informative pattern on the list — provided it is real. Two apparent clusters in a six-shot group are one of the commonest small-sample illusions in shooting, so look for the split in ten shots or more before you trust it. A genuine split means the rifle was shooting well twice, in two different states. The usual explanations are a pellet change or a mixed tin halfway through, a fill top-up that moved the rifle onto a different part of its pressure curve, a change of position or rest between shots, or a scope mount slipping and settling.
How to confirm: shot order is everything here. If shots 1–3 are one cluster and 4–6 the other, whatever you did between shot 3 and shot 4 is your cause. If the two clusters interleave in time, suspect the pellets rather than the rifle.
6. Tight but off-centre
Not a dispersion problem. Either your zero is off — or you weren't at your zero distance.
Worth including because it is so often misread as poor shooting. If the group is tight and simply sits somewhere other than where you aimed, the rifle and the pellet are doing their job. Nothing about the pellet choice needs to change.
First, though — were you at your zero distance? A sub-12 ft·lb pellet flies an arc with two zeros, so a tight group printing low at 15 or 45 yards from a 30-yard zero is correct trajectory, not a zero error. Dial that out and you will ruin a good zero. If you were at your zero distance and the group still sits off the aim point, then the scope is pointing somewhere slightly different from where the pellet is going.
How to confirm: measure the offset from the aim point to the centre of the group, convert it to turret clicks, and dial it out. How to zero an air rifle scope walks through it, and Pellet does the arithmetic for you — see below.
Quick reference
| Shape | Most likely cause | First check |
|---|---|---|
| Vertical string | Velocity variation | Chronograph — extreme spread |
| Horizontal string | Wind, cant or hold | Repeat in calm conditions |
| Round but wide | Pellet fit or quality | Pellet test against alternatives |
| Tight plus a flier | Damaged pellet or a pulled shot | Log lot numbers; call your shots |
| Two clusters | Something changed mid-string | Shot order — what happened between them |
| Tight but off-centre | Zero — or holdover at a non-zero distance | Confirm the distance, then measure the offset |
Change one thing at a time. The single biggest reason shooters never work out what was wrong is that they swap the pellet, adjust the regulator and change their hold in the same session. Whatever the shape suggested, alter one variable, shoot another group of the same size at the same distance, and compare. That is slower for one afternoon and very much faster over a season.
Pellet reads the shape for you
Everything above is a skill, and like any skill it takes a lot of targets before it becomes instinct. That is the part Pellet is built to shortcut.
Photograph the target and the app finds the pellet holes, tells you how many it detected against how many it expected, and lets you mark or refine any it missed. It scales the image from references printed on the card itself — a ruler or a millimetre grid — so it isn't tied to one brand of target: a commercial card carrying a printed scale works fine. You get the group size in millimetres and in MRAD, and a rating band.
Then it reads the pattern. Underneath the measurement is a plain-English diagnostic that comments on the shape of the group and attributes a likely mechanical cause — the kind of reasoning this page has just walked through, applied to your actual target. An excerpt from a real analysis:
"The vertical stringing here points to velocity drift across your fill charge rather…"
And where the shape turns out to be a zero problem rather than a grouping problem, the app says so in the most useful possible terms: a ZERO CORRECTION panel giving elevation and windage separately, each in millimetres, MRAD and scope clicks, with the direction to turn. When the correction works out below one click it tells you zero clicks rather than inventing an adjustment you don't need.
An instrument measures. A coach explains. Pellet does both — the group measured in millimetres and MRAD, the shape read for you, and the correction handed over in clicks. Pellet is in development for iOS and isn't released yet; the waitlist is how you hear first.
Join the waitlist →
Common questions
Why is my air rifle grouping vertically?
Usually shot-to-shot velocity variation rather than aim. On a PCP that most often means fill pressure moving outside the regulated or sweet-spot band across the string, a regulator settling or creeping, or a temperature change during the session. Inconsistent hold and follow-through can produce it too. Chronograph the string and look at extreme spread — if velocity is wandering, the shape is a velocity problem, not a shooting problem.
What causes horizontal stringing on a group?
Wind first, especially if the shots walk progressively in one direction as a breeze builds. If it was genuinely still, look at cant and cheek pressure — a rifle rolled slightly differently from shot to shot moves the point of impact sideways, and so does an inconsistent hold on a light sporter.
Should I ignore a flier?
Only if you can say why it happened. A shot you called bad as you released it is a shooter flier and is fair to note and set aside. A shot you can't account for is data, and discarding it quietly makes your groups look better than your shooting is.
How many shots do I need before the group shape means anything?
Three shots can look like almost any shape by chance. Five is a workable minimum for spotting a pattern and ten is much better, particularly when comparing pellets. The more shots in the group, the less likely the shape is simply an accident of small numbers.