For final "qualification" of a load, I shoot no less than 10 shots, and calculate the 50 and 90 percentile group sizes. During working up the load, for example COAL test, I even shoot 2-shot groups. If it looks promising, I will fire more shots to confirm, or I will move in to other configurations. Not ideal, but have to strike a balance between ideality and practicality.
If only extreme-to-extreme group size is measured, it is indeed no point shooting more as the group can't shrink.
-TL
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