Another comment is that most handloaders calculate the SD of far too few shots to be meaningful, often just because there's a SD function on their chronograph. The ammo factories calculate SD from several dozen shots, and sometimes even more for match ammo, not three or five or even 10. It's often illuminating to calculate the SD of two separate 5-shot strings of the same load. The difference can be considerable!
Another factor is that most of the "affordable" chronographs handloaders use have too little screen spacing to provide consistent velocities for individual shots, so any SD calculations are just about meaningless. The average for 10 shots may be very close to the average from chronograph with a much longer screen spacing, but the individual shots will differ considerably. I know this partly from lining up more than one small chronograph with my Oehler 35P and recording the velocity of each shot from both chronographs.
