Velvet
Well-Known Member
- Joined
- Nov 5, 2017
- Messages
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well thought
Can SD and ES be a shortcut for accuracy
- Thread starter CA48
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J E Custom
Well-Known Member
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
25WSM
Well-Known Member
Low SD/ES is absolutely not required to shoot good at 1000 yards. When I first started shooting 1000 yard matches I thought you did. I told one of the world record holders that my load had a 4 SD and he said it doesn't mean anything. He told me lots of his 1000 yard loads have 20 to 30 SD. He also told me that his really good 1000 yard loads that shoot 4 inches for 10 shots shoot like crap at 100 yards. Like crap I mean 1 inch. You really have to do a ladder test at your longest distance to get the vertical out. It may have a low SD or it may not. But if they show no vertical who cares. Timing the accuracy node is the absolute most important factor. It will give you vertical compensation when you have it right. Ladder test will tell you if your there. I always use the Satterly method to find nodes then I use seating depth to fine tune accuracy. Then I ladder test above and below that load to fine tune the vertical. Shep
DUSTY NOGGIN
Well-Known Member
a 5 shot group that shot 2971, 2971, 2971 , 2971 and a 3021
would be a 20 sd and a 50 ES
but id really wanna know what caused that 3021.. but they all count ..
would be a 20 sd and a 50 ES
but id really wanna know what caused that 3021.. but they all count ..
25WSM
Well-Known Member
Did you notice any bullet seating harder than the rest. Neck tension causes a lot of the inconsistency.
DUSTY NOGGIN
Well-Known Member
that was just for topic ..
im all for the low es though .. ive been lucky to find good accuracy with all my low sd/es
- 1. Work out the Mean (the simple average of the numbers)
- 2. Then for each number: subtract the Mean and square the result
- 3. Then work out the mean of those squared differences.
- 4. Take the square root of that and we are done!
- THATS the formula for SD. A little more to it than averaging.
- That's why I said I'm too dumb to calculate it
