Thread: Let's talk about velocity Extreme Spread (ES)

Originally Posted by No.3

This is mostly a discussion about which statistical measure is the most useful for the purposes of assessing what we want to assess - one tool the pros use (think election polling and the like here) is the calculated probable margin of error in the sample size. This is another useful way to assess if the info generated from a sample size is going to be reliable over the long term.

For our purposes on the topic of reloading and shooting, I feel that MV SD and ES are two different measurements and both give us potentially useful information but answering a different question. MV SD (or specifically a low figure) is an indication that if the group size is acceptable, the likelihood of a reliable and predictable impact point each time you pull the trigger is greater. A high ES figure indicates that the potential for a higher vertical spread of impact points on target is possible, everything else being equal. Ideally, you want as low an ES as possible, as low a MV SD as possible, and a load that performs with a small group size as possible. While using the pill design that you want, at the velocity you want, with a reliable supply of components, and not eating the insides of things.

Not much of an ask.

No. ES and SD are different ways of measuring the same thing. SD is better at it. ES tells you nothing that SD does not, and tells you less. Use SD if you care about measuring your velocity consistency. It is easy to calculate and all modern chronographs do it for you. Get a sample of at least 10 shots. End.