Thanks creeper, I'm not competing. I won't get into neck turning, too much effort:-). I am culling the cases exactly as you indicated, had some very good results today virtually no horizontal dispersion across two loads (36.5&37 gr varget) and some minor vertical stringing, less the.4 and the velocity extremes seem to coincide with the stringing. Ss you would expect. So, i don't think powder variation is a concern, both groups over lap perfectly. My guess is neck tension, I could feel slight variations in tension during bullet seating. Trying to asses if it's worth scrutinizing my case weight more or just caulk it up to tension.
My Stdev is 25, extreme spread 59 avg velocity 3643 for 36.5 gr. 22-250