Humor a NUB. What is SD and ES? How do you calculate it?
There have been lots of good explanations and maybe this will make them clearer.
First the reason for SD and ES.
Standard Deviation = SDs Are the average of all velocities in a string/batch of loads. normally a minimum of 5 or more shots are required
Extreme spread = Relates to the lowest velocity to the highest velocity in a batch/load. you can get an ES with only 2 shots but 5+
will give you better numbers for that load.
Both SD and ES are for predicting the consistency of a load and if it will be dependable all the time. You can have fairly low SD s and have one shot that raises the ES because it was out of the normal range of velocities and not effect the SD s two much because the other shots were very close together. (Many times this causes a flier).
For hunting or target both are important to be able to predict the Point of impact range of dispersion. (Group for short).
Both SD s and ES s can only be determined by a chronograph. One is all you need, but if the velocities are well off the listed, sometimes it helps to use a second one to verify.
These numbers don't need distance to be a viable factor because they are measured at the muzzle or within a few yards for accurate numbers. velocities at difference yards tells you more about the bullet performance and it's ability to move through the air.
Grouping at 100 yards gives the best example of the rifles potential accuracy with out a lot of shooter error and bullet performance. After all testing at 100 yards, you must then test the best load you have at longer ranges to verify its consistency at all usable distances.
SD s And ES s are just two of the many tools we use to build confidence in out ammo and be comfortable with our first shot or our last.
J E CUSTOM