L:So my SK+ has a smaller SD than my Center-X, but a larger ES. That's why it can hold smaller groups closer, but just miss the target or have drastically large group due to a flyer or two.
Center-X had a ES of 20, SD of 10.
SK had a ES of 30, SD of 8.
ES of 20 vs 30 would mean a 2" vs a 3" group at 200.
I am not sure what a 10ES difference at 50/100 yards would mean, but it's not that drastic.
If variation in MV were the determining factor in CTC group precision, then the ES of the MV would determine the CTC group precision at all distances. If I understand correctly, your observation is the CTC precision of a group correlates with, but is not determined by, the SD of the MV at 50 yd and therefore presumably at distances less than 50 yd. Interesting.
Rick