The assumption that's being made here is that the cross hairs are, or were in the center of the group for each shot. What we're contending with here, as you know, are two systems of variation, or noise. There is the variation of the reticle about the target, and the variation of impacts about the reticle. Strangely we tend to blame both systems on the later while suffering from the inability to address the variation of the former. On the mentioned test platform above an 8x32 power Nikon scope is the sight. At 100 yards I can still see slight movements in the reticle about the target. I don't think it's fair to the ammunition to go ape crazy on gaussian distributions for load worthiness estimation when the launching pad is adding considerable noise. I also don't think 3 standard deviations, or 30% scatter is true for all guns and shooters. For a very accurate BR rifle I doubt the competitors would find that amount of variation acceptable.
