Reading your shot groups

• Judge a group by its size before its place: a small group means a consistent shot.
• Measure size as extreme spread or mean radius, and compare groups of the same number of shots.
• Turn the sights only for a tight group off the centre, and move its centre, never a single shot.
• A pattern tells you what to check first, not what went wrong.
• Judge progress over weeks and many groups, shot in the same conditions.

A group’s size says how much your shots vary. Its centre, the mean point of impact, is the average of where they landed. The NSRA tells beginners to aim for consistency first: the smaller the group, the better you are shooting.

The two call for different fixes. For a large group, check your hold and your shot first, then the rifle and the pellet. For a tight group in the wrong place, check the sights, and keep them right: coaching material from the CMP finds that failing to keep the rifle zeroed is one of the commonest and costliest errors of less experienced shooters.

Before you go forward to a card, unload, leave the action open, and at a club wait for the range officer’s word. To find the centre by eye, the CMP draws a line through the group each way, real or imagined; where they cross is the centre, leaving out a flier that is clearly out of the group. How each hole is scored is on the ISSF 10 m air rifle target page.

Extreme spread is the distance between the centres of the two shots furthest apart. Mean radius is the average distance from each shot to the group’s centre. As the notes to the shotGroups statistics package point out, the mean distance to the centre uses every shot; extreme spread rests on two.

On paper, measure extreme spread from the outside edge of one hole to the outside edge of the other, and take off one hole’s width. Mean radius needs every hole’s position, which is work for software.

Here the centre is the average: (5 + 1 + 3 + 4 + 2) ÷ 5 = 3 mm right and (4 + 4 + 2 + 5 + 5) ÷ 5 = 4 mm low, 5 mm from the middle of the card. The mean radius is (2.0 + 2.0 + 2.0 + 1.4 + 1.4) ÷ 5, about 1.8 mm. The extreme spread, between shots 1 and 2, is 4 mm.

Add a sixth shot, 3 mm right and 10 mm low. The extreme spread doubles to 8 mm, between shots 3 and 6; the centre moves to 5 mm low, and the mean radius rises by more than a third, to 2.4 mm. One wide shot sets the extreme spread on its own, while the mean radius weighs every shot, which makes it the better measure to follow over time.

A group’s shape can point at what to check first. Each cause below is one possibility among several, and apart from the first, only a shape that repeats over several groups is worth acting on.

• Tight, but off the centre: the sights. The CMP adjusts them after a single group, as below.
• Tight, with one shot away: ask what happened on that shot. SvSF’s course material says the faults that put a shot where you did not mean it arise most often at the moment of firing, so it teaches you to read the sight picture as the shot goes and call where it will land before you look. If you called it wide, the shot is the likeliest cause; if you called it good, the pellet is one thing to check (Air rifle pellets).
• Wider than tall, standing: not a fault by itself. ISSF coach-course material notes that trained shooters’ groups are bigger horizontally than vertically.
• Taller than wide: one possible cause is firing at different points in your breath; SvSF has you breathe out until the bull sits in the ring of the front sight, stop there, and aim and fire in that pause. Another is a head, left hand or grip placed differently from shot to shot: the same ISSF material describes how moving each of them moves the rifle’s natural point of aim up or down.
• Large, with no shape: one possible cause is a hold or a shot process that is not yet repeatable; start with Air rifle positions.
• A good group that wanders during a session or from day to day: the CMP notes that zeroes change from day to day, during a session and between positions.

Charts that give each part of the target its own fault, such as low left for a jerked trigger, circulate online; the pistol correction chart is the best known. None of the coaching material this post draws on uses one, and we found no coaching body that publishes one for the rifle. Read one as a list of things to check, never as a diagnosis.

Sights move the centre of a group, never a single shot. The CMP’s rule: move the rear sight in the direction the group must go, so a group low and right needs the sight moved up and to the left. In its coaching, new shooters fire a whole group of five before they adjust.

Read your own sight’s arrows first. The CMP explains that sights made in the USA usually mark where the group will move, and many made in Europe where the shots are now. Feinwerkbau’s Model 800 manual is one: when you are shooting high, you turn the elevation screw towards H.

What one click moves is the maker’s figure, and it depends on the sight and on the sight length, the distance from the rear sight to the front sight. Feinwerkbau gives about 0.2 mm at 10 m for the Model 800, with a sight length of about 950 mm. Anschütz’s table for its 8000 series gives, at 10 m and 800 mm, 0.48 mm a click for the 8012 and 0.24 mm for the 8024.

In the example, the centre sits 3 mm right and 4 mm low. At about 0.2 mm a click, that is an estimate of 20 clicks to bring the group up (4 ÷ 0.2) and 15 to bring it left (3 ÷ 0.2); at 0.48 mm, about 8 and 6. Make the change, shoot another group and expect to adjust again: the CMP calls zeroing an art, not an exact science. Since zeroes change from day to day, check yours with your sighting shots each session.

Leave the sights alone while your groups are wide. The CMP warns that accurate sight adjustment needs reasonably good groups to start with. A scattered group’s centre moves from one group to the next, so a correction worked out from it is mostly chance. Once your groups are reasonably good, the CMP has you check every group and adjust whenever it is not centred, then shoot another group to check.

Call every shot before you look. When your calls and your holes agree, your sights are probably right, and the wide shots are yours to work on. SvSF puts the goal simply: good shots in the middle, bad shots to the side.

Change one thing at a time in your position or technique, then test it, as TRA advises, with your coach if you have one. Give the test several groups, on more than one day.

One card proves little. The shotGroups notes point out that measures such as extreme spread grow, on average, with the number of shots in a group, so compare five-shot groups only with five-shot groups. Assuming the shots scatter in a bell curve (a normal distribution), the same in every direction around the centre, its tables need about 100 shots in groups of five to pin down your true spread by extreme spread to within about 10 % either way, with 90 % confidence. Estimating the spread from every shot’s position instead needs somewhat fewer, about 90.

• Keep the conditions the same: rifle, pellet, distance, position and, as far as you can, the light.
• Keep a diary. TRA suggests noting after each session any change to your position or technique, the range, the weather, the scores and the equipment settings, and following your scores week by week. The CMP’s Shooter’s Journal adds the pellets and the clicks you moved the sights.
• Follow the average over several sessions, not the best card or the worst.

For every scan, Shooter shows where the shots landed and the group’s mean radius, spread and impact point. What the numbers say about your technique is for you and your coach to read.

Should I use extreme spread or mean radius?

Both, for different things. Extreme spread is quick to measure on paper and shows your widest pair of shots. Mean radius uses every shot, so a single flier moves it less, which suits tracking. Compare either only between groups with the same number of shots.

How many clicks do I need to centre my group?

Divide how far the group’s centre sits up or down, and then left or right, from the middle of the card by your sight’s click value. Feinwerkbau and Anschütz give it for a stated sight length: Feinwerkbau in its Model 800 manual, Anschütz in a table on its website. Feinwerkbau gives about 0.2 mm a click at 10 m with a sight length of about 950 mm, so 4 mm low is about 20 clicks up. Then shoot another group to check.