Measuring Shot-to-Shot Consistency
No two shots leave the muzzle at exactly the same velocity, and that variation matters because inconsistent speed becomes inconsistent drop and drift at distance. Analysts summarize this scatter with simple statistics drawn from a string of chronographed shots. The two most common measures are extreme spread and standard deviation, and each tells a different part of the story.
Extreme Spread
Extreme spread is the plain difference between the fastest and slowest velocities recorded in a group. It is easy to understand and quick to compute, but it is fragile: it depends only on the two most extreme shots and ignores everything in between. A single unusual reading can inflate the extreme spread even when most shots were tightly clustered.
Standard Deviation
Standard deviation describes how tightly all the velocities cluster around their average, giving every shot a voice rather than only the extremes. A small standard deviation means the string was consistent, while a large one signals scattered performance. Because it uses the whole data set, it is more stable and more meaningful than extreme spread, especially as the number of shots grows.
Why Sample Size Matters
Both statistics become more trustworthy as more shots are recorded. A three-shot string can badly understate true variation simply because it had few chances to catch a slow or fast round. Larger strings, often ten shots or more, give standard deviation room to converge on the load's real consistency and make extreme spread less of a lottery.
How Velocity Scatter Reaches the Target
Velocity variation translates into vertical scatter downrange, because a faster shot drops less and a slower shot drops more over the same distance. This vertical dispersion grows with range and with time of flight, so a load with tight velocity numbers produces more predictable elevation far away, even when near-target groups look identical.
Worked Example
Imagine ten shots averaging 2,750 feet per second. If nine fall within a few feet per second of the mean but one reads 2,700, the extreme spread jumps to 50 feet per second, painting a bleak picture. The standard deviation, drawing on all ten shots, might still be a modest 12 feet per second, correctly showing that the string was mostly consistent apart from one outlier.
A Common Misconception
A frequent error is judging a load's consistency by extreme spread from a tiny three-shot string. With so few shots, extreme spread is dominated by chance and reveals little about typical behavior. Standard deviation over a larger sample gives a far more reliable picture, and treating a lucky small-sample spread as proof of quality invites disappointment at long range.