247sniper Posted April 8, 2012 Report Share Posted April 8, 2012 Can someone explain this for me please, If a average MV is 974, the lowest verlocity recorded was 971 and the highest was 978 over 10 shots. What the standard deviation explained please, Cheers lads Steve. Link to comment Share on other sites More sharing options...
brown dog Posted April 8, 2012 Report Share Posted April 8, 2012 Steve, Two different things; extreme spread - standard deviation. Extreme spread is simply lowest value to highest value. Standard deviation is a statistical measure that's a bit more complicated; probably best to read through this: http://www.robertniles.com/stats/stdev.shtml Link to comment Share on other sites More sharing options...
Chris-NZ Posted April 9, 2012 Report Share Posted April 9, 2012 That ref is all very well BD but it's got sod-all practical value for most shooters. I used to know all that crud when I was tutoring stats but most (happily) well forgotten now. One other way to interpret an SD is: - 68% of values will fall within +/- 1 SD of the average value - 95% will fall within +/- 2 SD - 99% will fall within +/- 3 SD Remember this level of certainty applies only for a large sample. ES is a more useful measure for most people. It gives the worst cases scenario at both ends and that probably counts for more. Chris-NZ Link to comment Share on other sites More sharing options...
brown dog Posted April 9, 2012 Report Share Posted April 9, 2012 That ref is all very well BD but it's got sod-all practical value for most shooters. I used to know all that crud when I was tutoring stats but most (happily) well forgotten now. One other way to interpret an SD is: - 68% of values will fall within +/- 1 SD of the average value - 95% will fall within +/- 2 SD - 99% will fall within +/- 3 SD Remember this level of certainty applies only for a large sample. ES is a more useful measure for most people. It gives the worst cases scenario at both ends and that probably counts for more. Chris-NZ umm? : Link to comment Share on other sites More sharing options...
Chris-NZ Posted April 9, 2012 Report Share Posted April 9, 2012 Didn't even read it BD- got bored in the first three lines.. Link to comment Share on other sites More sharing options...
brown dog Posted April 9, 2012 Report Share Posted April 9, 2012 Didn't even read it BD- got bored in the first three lines.. Link to comment Share on other sites More sharing options...
achosenman Posted April 9, 2012 Report Share Posted April 9, 2012 Try this. He makes it understandable. Click Link to comment Share on other sites More sharing options...
desparado Posted April 9, 2012 Report Share Posted April 9, 2012 Can someone explain this for me please, If a average MV is 974, the lowest verlocity recorded was 971 and the highest was 978 over 10 shots. What the standard deviation explained please, Cheers lads Steve. Steve, Does your Chrono' not produce the SD figure for you? I'd have thought most new models nowadays would do it. Putting my Statto hat on, basically SD is a more meaningful way of comparing ES between different calibres - you still want it to be as small as poss'. Cheers, Link to comment Share on other sites More sharing options...
247sniper Posted April 9, 2012 Author Report Share Posted April 9, 2012 Steve, Does your Chrono' not produce the SD figure for you? I'd have thought most new models nowadays would do it. Putting my Statto hat on, basically SD is a more meaningful way of comparing ES between different calibres - you still want it to be as small as poss'. Cheers, No mate, my chrono gives me the highest, the lowest, shot count and the average between the amount fired. I thought that it was most important that the ES was small as possible, lucky enough on the .204 with the load I have developed it is Cheers fella, Steve. Link to comment Share on other sites More sharing options...
jcampbellsmith Posted May 31, 2012 Report Share Posted May 31, 2012 ..ES is a more useful measure for most people.... Chris. ES only tells you the difference in velocity between your fastest and slowest shot, nothing else. It tells you nothing more whether you fire two shots or a 100 shots. Here's an interesting link on the topic: http://riflemansjournal.blogspot.co.uk/2010/02/reloading-velocity-decisions.html Regards JCS Link to comment Share on other sites More sharing options...
Laurie Posted May 31, 2012 Report Share Posted May 31, 2012 You find that the SD is usually half the extreme spread value on small samples (ie 5). To calculate the SD you'd need all of the readings in the string, but as the ES is 7 fps, the SD will almost certainly be either 3 or 4 if it's from 10 rounds or less. To have any value, there must be a large sample size. You don't say how many rounds were fired, but a 7 fps ES would be regarded as excellent in most applications assuming you fired at least five, even better from ten. If it was from 3 rounds, both SD and ES are pretty meaningless. (In my pet hate cartridge .22 Hornet, I got some 5-shot strings that had 3 consecutive shots with identical MVs, a fourth only a few fps different and a fifth 100 or more fps awry!) Link to comment Share on other sites More sharing options...
Chris-NZ Posted June 1, 2012 Report Share Posted June 1, 2012 The Hornet is my pet-hate chambering too Laurie. That's why I ditched it It was funny doing .308s or .270 after handling Hornet cases- a world removed. I just stick with the suppressed .223 now- far easier to load for. Chris-NZ Link to comment Share on other sites More sharing options...
Andrew Posted June 1, 2012 Report Share Posted June 1, 2012 Can someone explain this for me please, If a average MV is 974, the lowest verlocity recorded was 971 and the highest was 978 over 10 shots. What the standard deviation explained please, Cheers lads Steve. It is a number that gives the statistical probability that your velocity will fall into a given range either side of the average. You can figure it out yourself: Take all the velocities for the string you measured and for each velocity, find the difference from the average. Take this difference and square it. Add all these squared differences together and divide by the number of shots minus one. (Divide by 9 for a 10 shot string, or 99 for a 100 shot string) Even a 10 shot string is a small sampling, normally, but your load seems to be under control!~Andrew Link to comment Share on other sites More sharing options...
jcampbellsmith Posted June 1, 2012 Report Share Posted June 1, 2012 Steve Use Excel. Send me an e-mail and I will send you back a spreadsheet to use. Regards JCS Link to comment Share on other sites More sharing options...
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