Calculating standard of deviation

[dmy]

I chronographed several different rifle loads last week. Five-shot groups and documented each round in fps. How does one calculate the standard of deviation for these groups? Is is as simple as subtracting the slowest from the highest and comparing that delta to the average velocity?

[RookieShooter]

Here is a Standard Deviation Calculator.

http://www.calculator.net/standard-deviation-calculator.html

[Whiterabbit]

If you have a standard population, half range (ES divided by two) is going to be pretty close to SD. Bottom line though, you can type "standard deviation" into google and get your equation.

Even easier, put the numbers in excel. The program will do the work for you.

I suggest looking at ES. IMO it is more useful when the goal is every-round-matters. If you are looking for great accuracy and you don't mind, say, putting down an amazing 9 round group and one shot that flies out into the ether, and are willing to just dismiss that shot, then IMO SD is better.

[Ubermcoupe]

If you have a standard population, half range (ES divided by two) is going to be pretty close to SD. Bottom line though, you can type "standard deviation" into google and get your equation.

Even easier, put the numbers in excel. The program will do the work for you.

I suggest looking at ES. IMO it is more useful when the goal is every-round-matters. If you are looking for great accuracy and you don't mind, say, putting down an amazing 9 round group and one shot that flies out into the ether, and are willing to just dismiss that shot, then IMO SD is better.

This is probably the easiest way to track my loads and info - set up the excel, get the scripts in order, then input the load info & results.

In the age of google, everyone can become pretty proficient with excel

[bsumoba]

IMO, don't worry about SD and pay attention to ES (extreme spread [highest velocity - lowest velocity]).

Try to get the ES as close to single digit numbers or in the teens. SD is usually about half of your ES number.

[Fastattack]

Not to be harsh, but since you don't know what it is, you should probably either do your homework or ignore it. At this point in your knowledge base it is just a number.

[dmy]

Thanks

Thanks. Almost everyone was helpful. Fastattack - pardon me for trying to learn more from this site. I guess your name could not be more appropriate.

[mjmagee67]

Or if you want a "close enough" approximation, take the extreme spread (high - low) and divide by 3. This will give you a number close enough for anything we do in shooting and reloading.

[Whiterabbit]

Another point to remember:

That most calgunners who claim their rifles are sub-MOA or show pretty pictures of ragged-hole groups are showing you the best their rifle does on one day that one time shooting well that day and no wind, etc. Very unlikely that any of the rifles we brag about doing this do it on command, every day.

Thus: remember calgunners will brag about their ES the same way. Don't be discouraged if you are getting ES's in the 20-30's and someone here claims they get 5 fps all day every day.

[Whiterabbit]

ES divided by 2 is a number I see used more often than 3. Actually I have never seen divide by 3. I have seen SD pretty close to divide by 3 though.

I'd still consider using the full ES though.

[Magilla26]

Most hand held scientific calculators have statistics built in. The quick reference card will show you how to enter a data set and calculate mean and standard deviation. These calculators are inexpensive. If your chronograph is like mine and only gives velocity, a scientific calculator will help you out.

[tanks]

Another point to remember:

That most calgunners who claim their rifles are sub-MOA or show pretty pictures of ragged-hole groups are showing you the best their rifle does on one day that one time shooting well that day and no wind, etc. Very unlikely that any of the rifles we brag about doing this do it on command, every day.
...

Well, that makes sense though in developing loads etc.. We want to find out the best the rifle could do in optimum conditions. Field conditions will adjust that for the worse.

[JagerDog]

Another point to remember:

That most calgunners who claim their rifles are sub-MOA or show pretty pictures of ragged-hole groups are showing you the best their rifle does on one day that one time shooting well that day and no wind, etc. Very unlikely that any of the rifles we brag about doing this do it on command, every day.

Thus: remember calgunners will brag about their ES the same way. Don't be discouraged if you are getting ES's in the 20-30's and someone here claims they get 5 fps all day every day.

I'll add everyone except those I see at the range are consistently sub MOA.

[Fastattack]

Thanks. Almost everyone was helpful. Fastattack - pardon me for trying to learn more from this site. I guess your name could not be more appropriate.

I'm sorry that I offended you, it wasn't my intent. From your question, I surmised you weren't asking to learn anything. You wanted to calculate a number. A simple google search would give you a wealth of knowledge instead of having someone else on this forum do it for you. If you had a specific question about how it applies, sample set size, or whatever that would be different.

[Whiterabbit]

I'll add everyone except those I see at the range are consistently sub MOA.

We must go to the same range. Did I ever tell you every rifle I own is sub MOA too?