To find the ES (extreme spread) and SD (standard deviation) you have to have a chronograph because you have to measure the bullets speed. The extreme spread is the difference between the fastest and slowest speed in a string of shots. Standard deviation is a formula you can calc it here http://www.calculator.net/standard-devia...lator.html or setup a spreadsheet to do it. Good groups also. Also forgot to add most chronographs will figure it for you.
Dave
Dave