? on ES / SD

[piutemike]

In working up loads today for my 300RUM the best one I found with the 180 E-Tip was 96.2 gr. retumbo. I shot 2 groups with that load .632 and .685. Both groups were 3 shot groups. The velocity of those 6 shots was between 3284 and 3270, a ES of 14.

My question is this, how do I figure the SD? Is there a simple way to do this? My chrono does not have this feature.

I was quite pleased with these groups since it is a factory gun, skim bedded, trigger tuned, muzzle break and wyatts box added by Shawn and I don't consider myself a good shooter.

Mike

[boomtube]

Statistically, computing Standard Deviation on a sampling of only three data points is meaningless.

[Buffalobob]

If you keep a record of your velocities once you get about 10 of them, you can enter them into Excell. Highlight them and then click on the little arrow to the right of the Sum symbol (sigma) and when it asks you if you want more functions, then click that and at the bottom is STDEV. Click that and you are done.

Std Dev as mentioned is not much use for a limited number of rounds.

[piutemike]

Thank you very much for your answers. I'll shoot some more tomorrow and use Excel as recommended.

Mike

[goodgrouper]

On a 3 shot group, the standard deviation will always be half of the extreme spread.

And I disagree with the other posters. If used in a load development ladder of .5 grain increments, a three shot group method will tell you what to re-test by showing you the nodes. If the SD stays good again on a different day, you have a winner for that temperature range 95% of the time.

In other words, a 5 shot group on one day is less meaningful than two 3 shot groups on two different days.

[Mikecr]

Why would you want SD anyway?
You have ES, and that's all that matters.

If I put a chrono on the market today, it would not display SD or any other monkey math. Just the raw, brutal truth..

[piutemike]

Just wanted to know how to figure SD. I did not know if there was a simple way of doing that.