Extreme Spread
Also: ES
The difference between the fastest and slowest muzzle velocity in a string of shots. Low ES is a foundational signal of a consistent handload.
Fire ten rounds across a chronograph, take the highest velocity minus the lowest, and that’s ES. For a precision load, single-digit ES (under 10 fps) is a target. Double-digit but under 20 is acceptable. Over 30 is a load that hasn’t settled.
ES is more sensitive to outliers than SD. One squib or one over-pressure round will inflate ES but move SD only a little. It helps to read both numbers together, because they tell you different things about the string.