Measuring accuracy honestly: groups, averages and sample size

Everybody has seen the photo: a tiny three-shot group next to a coin, captioned "sub-MOA." It's a great feeling to shoot a group like that. The trouble is that one small group says very little about how the rifle, the ammo, or the shooter will actually perform the next time.

If you want to know how accurate your setup really is, you need a better way to measure it.

Quick definitions

• Group: a set of shots fired at the same aim point.
• Extreme spread (ES): the distance between the centers of the two shots farthest apart. This is the "group size" most people quote.
• MOA (minute of angle): an angle, roughly one inch at 100 yards. Groups are often described this way so you can compare them at different distances.
• Mean radius: the average distance of every shot from the center of the group.

Why 3-shot groups lie

Shooting is full of small, random variation: tiny differences in ammo, barrel heat, your wobble, the wind. Every group is a sample of that randomness.

With only three shots, luck plays a big role. Sometimes three shots land close by chance. Sometimes one wanders. So a single 3-shot group can make a so-so rifle look amazing, or a good rifle look bad.

There's also a selection problem. If you shoot five 3-shot groups and post the best one, you've shown what the rifle does on its luckiest day, not what it does normally.

More shots per group, and more groups total, give you a truer picture. Groups tend to get bigger as you add shots, because you're giving the rare flyer more chances to show up. That's not bad news. It's the real answer.

Extreme spread vs. mean radius

Extreme spread is simple to measure, but it only uses two shots: the two farthest apart. Every other shot in the group is ignored. One flyer can double the number.

Mean radius uses every shot. It tells you, on average, how far a shot lands from the center. That makes it a steadier number that changes less from group to group, which is exactly what you want when comparing loads or rifles.

Measuring mean radius by hand is tedious. Several phone apps and computer programs let you photograph a target, mark each hole, and calculate it for you.

Measure	Uses	Strength	Weakness
Extreme spread	2 shots	Easy to measure	Heavily swayed by one shot
Mean radius	All shots	More consistent, more informative	Needs an app or some math

Sample size: how many shots is enough?

There's no magic number, and experienced shooters disagree on exactly where to draw the line. But the general principle is clear: more data means more confidence.

Some practical guidelines:

• Use more than 3 shots per group. Five is better. Ten is better still.
• Shoot multiple groups. Several 5-shot groups tell you far more than one.
• Look at the total. Many serious testers combine all their shots into one composite group (overlaying groups on the same center) and measure that. It's a more honest picture of real-world dispersion.
• Be skeptical of small differences. If load A beats load B by a tiny margin on a handful of shots, that may just be noise. Retest before you buy a case of anything.

A simple, honest testing method

Control what you can

• Solid, repeatable position. A good rest, consistent cheek weld, same setup every group.
• Clean, consistent barrel condition. Note whether the barrel is clean or fouled, and be consistent. Some rifles shoot differently for the first few rounds after cleaning.
• Barrel temperature. Let the barrel cool between groups, especially in desert heat where a hot barrel and hot sun stack up.
• Calm conditions. Wind adds dispersion that has nothing to do with the rifle.
• Same distance, clearly measured.

Run the test

1. Decide how many shots and groups you'll fire before you start. Don't stop early because the first group looked great.
2. Fire every planned group, including the ugly ones.
3. Record every group. No cherry-picking.
4. Measure mean radius (and extreme spread, if you like) for each group and for the composite.
5. Compare averages, not bests.

Be honest about the shooter

The rifle and ammo are only part of the equation. Fatigue, trigger control and position all show up on paper. If you're testing gear, shoot when you're fresh. If results are inconsistent, consider having another experienced shooter try it too.

What "accurate enough" means

For hunting, practical shooting and most real-world uses, consistency matters more than a record-setting group. A rifle that reliably keeps every shot inside a modest circle is more useful than one that occasionally prints a tiny group and occasionally throws a flyer. Honest measurement helps you know which one you have.

Need a hand?

If groups suddenly open up or a rifle never seems to settle down, the cause might be mechanical: loose mounts, action screws, a worn barrel. Our gunsmithing service can take a look, and our training options can help tighten up the shooter side of the equation.