I am new too this program please can anyone tell me what Std Dev in the ballistics calculator and load infomation.

THanks
Steve

standard deviation. average crono deviation

O.K. I stated looking into this myself when I started reloading and purchased a chronograph. I am beginning to have a clue and that’s about it.

Std Dev. is primarily information regarding to the quality of your ammunition by measuring consistency of the velocity in a given amount of the same type of ammunition. It is derived is with a severely complex (to me anyway) mathematical equation. I have asked one of the Quality Control people at work and what she told me is essentially"A measure of the range of variation from an average of a group of measurements." and a graph looking like an upside down horse shoe with the average being at the center of the arc.

Meaning to me nothing! So I did a little more research and found an article at the website www.gun-tests.com/perf...otest.html that seems quite helpful (look under velocity).

What it is, is how close you can expect the velocity of each cartridge to stay close to the average of the all the cartridges fired (a measurement of the past to help predict the future.)

For example: the bullet leaving our firearm performs best for our needs at 1000 feet per second (fps). So we are looking for a an average velocity in our ammunition to be 1000 fps, So we found a box of 100 rounds of ammunition and fired 20 rounds of it that has an average of 1000 fps with a Standard Deviation of 20 fps, what this means is that 95.4% of all of the 80 remaining cartridges should (if fired under the same environmental factors) produce velocities from 980 fps to 1020 fps meaning higher quality than a higher standard deviation such as 40 fps.

I am still trying to figure out where they get 95.4% from, so until then I just look for and reload for low Standard Deviations.

Now how much this will affect you will depend on what you are trying to achieve. I have been told that the level of STD DEV only starts making differences at extended ranges, but I have noticed it on small-bore rim fire accuracy.

Hope I helped and if any one out there has a mathematical way of figuring out how the percentages are figured out please let me know.

A large standard deviation indicates that the data points are far from the mean (what jbird22cal calls "average") and a small standard deviation indicates that they are clustered closely around the mean.

Wikipedia has a great mathematical explanation.

FALPhil wrote:

A large standard deviation indicates that the data points are far from the mean (what jbird22cal calls "average") and a small standard deviation indicates that they are clustered closely around the mean. Wikipedia has a great mathematical explanation.

I do stand corrected. Thank you FALPhil!

that link for wikipedia is en.wikipedia.org/wiki/...deviation.

Std Dev is important, having an understanding of it and how it effects the over all performance over a group of ammunition is desirable to any shooter whom actually likes to hit targets. It is also a reflection as to the quality of reloaded ammunition, I find it a great challenge as a new reloader to match or beat the Std Dev of factory cartidges and consider it to aid in my own "tuning of cartridges" for my firearm.

One thing to remember about the SD numbers, the lowest SD does not always give you the most accurate load. However, when the group comes together into a very tight cluster and the SD dropps into the single digets, you have a winner.
Ed

Also if you use a crono you need to try and keep the ES down. This is important to having all things work. Certain Primers will give you different ES values.

thanks guys for your help