Correlation? Well, the word threw me off at first. The idea of adjusting the standard deviation for the actual magnitude of the measurements is certainly valid ... and appropriate. If I'm not mistaken, the correct term would be normalization or in the case of the resulting value "Normalized standard deviation." Correlation typically refers to the degree to which two variables are related. Just semantics ... the normalizing process that Kernel describes is quite reasonable. Kernel's rule of thumb, put another way, says that if your total range is less than 6% (+/- 3%)of your velocity, then your accuracy will be pretty good. This seemed a little too high to me, so I ran some numbers for a .308 at 100 and 200 yards. I was quite surprised to find that at 100 yards, +/- 3% variation in velocity contributes to a vertical range of just over .25 inches ... accurate enough for me! At 200 yards the contribution gets up to 1.25 inches ... but still pretty acceptable. Although the contribution due to velocity is increasing as the distance gets longer, even at 300 yards it is only about 3 inches of vertical variation. Just to see where it goes in the extreme, I looked at the 600 yard scenario: the same "normalized std dev" of 1% will contribute to 15.8 inches
of vertical dispersion. The bottom line is that the "s.d." should be a LOT more important to the long range shooters than it is to those of us who keep things a little closer in.
TGS ... Thanks for the interesting post.
Bill