Hi, copper:
Actually what dodgestdshift described is mean deviation or mean absolute deviation (MAD). Standard deviation is a bit more complicated. Average your velocities, then square the difference between each shot and the mean (average), add the squares, divide by the number of shots and take the square root of that. You can do some further analysis with the standard deviation that you can't do with the mean deviation.
In theory, 2/3s (68%)of your velocities will be within one stanard deviation of your mean, 95% within two standard deviations and 99% within three.
I worked out an example a while back, but that thread must have been lost when the server crashed several months ago. I'll do it again if you don't have a scienfitic calculator handy.
In some ways the extreme spread is more useful, since the bloopers and spikes are what you want to avoid.
What some folks call the ladder test is the best way to find a good load. Fire a series of shots at the same target as you work up a load. Likely the groups will move as you add powder. With luck, at some point they'll say put with another 1/2 grain increment. Your barrel is stable at this point and that's where you want to be. Now you may be well under the velocity you want and adding powder starts walking the groups again. In that case try a different powder or bullet weight. Sometimes another bullet of the same weight or primer or bullet seating depth make makes a big difference.
I like H322 in my .222, but there's one thing you should be careful about. There's been at least 4 versions sold. Surplus IMR 8208, Nobel from Scotland, early Australian and current Australian. If you look in several reloading manuals, you'll see 22.5 grains or 24.0 grains as MAX, with only Speer in between. Hornady #4 recommends 24.0 grains with their 50 grain bullets, but there's no way I can use that much early Australian in my old 700, even with V-Max Molys. The later Australian is slower, but I haven't pushed it yet.
Bye
Jack