QUOTE (locobob @ November 14th 2009 12:34 PM)

I think ES stands for "extreme spread".
Yup!
...and sorry bout' the shorthand. I should of said Extreme Spread 21 fps. I was typing off my field notes.
ES is not the same as SD (standard deviation).
To get the ES (Extreme Spread), the lowest velocity is subtracted from the highest velocity.
Most chronographs automatically give you both ES, SD and Average Velocity, # Shots, etc. (depending on the model) after each shot string.
Most factory ammo ES's are between 30-75 fps IME.
So a 21 is
really low and desirable. Over 75fps, at least IMHO, and you have to question quality control or quality of hand loads based on
many factors.