Data from: How many shots are enough? Optimizing precision measurements when testing lead-free ammunition

Growing concern about lead exposure in scavenging wildlife and the
consumers of game meat has increased interest in evaluating the
performance of lead-free rifle ammunition. Testing both accuracy and
precision helps ensure reliable shot placement while reducing the risk of
non-fatal woundings. However, precision testing methods vary across
studies, sometimes leading to contrasting interpretations of ammunition
performance. Using shooting range data from 37 rifle-ammunition
combinations tested under typical shooter-operated conditions, we
evaluated how precision estimates based on extreme spread and mean radius
change with increasing sample size and identified points of diminishing
returns. We also compared whether three 5-shot groups (3×5) or five 3-shot
groups (5×3) produce more reliable precision estimates. Mean radius
stabilized at relatively small group sizes (n = 9), whereas extreme spread
showed weaker evidence of stabilization. Additionally, 5×3 groups
underestimated 15-shot reference values more than 3×5 groups. Based on
these results, we outline best practices for evaluating ammunition
precision, including using at least 10 shot groups when feasible,
reporting both mean radius and extreme spread, favoring 3×5 designs over
5×3 designs, and testing across multiple rifles, while reporting barrel
twist rate and length, bullet mass and length, and muzzle velocity.