What’s the Best Way to Measure Rifle Accuracy? Group Size vs. Group Area vs. Mean Radius
When it comes to evaluating rifle accuracy, most shooters reach for their calipers and measure group size—the classic “center-to-center spread” of the two most distant shots. But is that really the best way to measure accuracy?
Today, we’re diving into the three main ways shooters measure precision:
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Group Size (Extreme Spread)
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Group Area
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Mean Radius (Average to Center)
We’ll explore how each method works, what it tells you, and which is most accurate and reliable for real-world shooting.
1. Group Size (Extreme Spread)
What it is:
Group size is the distance between the two farthest bullet holes in a group. It's simple and widely used.
Example:
You shoot five shots and measure from the center of the farthest two holes—say, 0.8 inches at 100 yards. That’s your group size.
Pros:
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Quick and easy to measure
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Widely accepted (especially in competitions)
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Requires only two points of measurement
Cons:
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Highly sensitive to flyers
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Ignores how tight the other shots were
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Doesn't reflect the “average” accuracy
Verdict:
Great for comparing maximum spread, but not always representative of overall precision.
2. Group Area (Bounding Box or Convex Hull)
What it is:
Group area measures the two-dimensional space that all shots occupy. Think of it as the smallest rectangle or shape that can contain all shots.
Pros:
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Captures both vertical and horizontal dispersion
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Useful for identifying directional trends (e.g., wind, cant)
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More data-rich than group size
Cons:
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Harder to calculate without software
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Still impacted by extreme shots
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Less standardized in the shooting community
Verdict:
Good for visualizing consistency and tracking trends over time, but impractical for everyday use without digital tools.
3. Mean Radius (Average Distance to Center)
What it is:
Mean radius is the average distance from each shot to the group’s center (center of impact). It represents how closely your shots cluster around the aim point.
How it's calculated:
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Find the center of impact (average X and Y of all shots)
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Measure distance from each shot to that center
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Take the average of those distances
Pros:
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Statistically sound and reliable
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Less affected by one bad shot (flyer)
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Reflects overall shot consistency
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Excellent for evaluating equipment or load testing
Cons:
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More complex to measure manually
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Requires data plotting or software
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Not often used in traditional shooting circles
Verdict:
The most accurate and meaningful metric for true rifle precision—especially for data-driven shooters.
For serious shooters, reloaders, and testers, mean radius is the most consistent and mathematically sound method of measuring precision. It gives a true sense of how tightly your rifle, ammo, and optic are working together.
However, group size still holds its place—especially in match settings and for quick visual comparisons. It's intuitive and easy, even if not always statistically robust.
Pro Tip: Combine Methods
You don’t have to pick just one. Here’s how the pros do it:
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Use group size for a quick, traditional benchmark.
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Use mean radius for deep accuracy analysis or when comparing loads, barrels, or conditions.
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Use group area if you want to spot directional inconsistencies (wind effect, shooter input, etc.).
Tools like Ballistic-X, OnTarget, or even custom spreadsheets make calculating these metrics faster and more precise.
Final Thoughts
If you’re chasing precision, especially at long range or in the world of rimfire/airgun competition, it’s time to go beyond basic group size. Mean radius provides a true, repeatable, and objective measure of accuracy—less vulnerable to flyers and more representative of how your system actually performs.
Next time you’re at the range, bring a ruler and a calculator. Your shooting data deserves better than just “that was a good group.”