nvshooter

December 22, 2006, 01:36 PM

I bought the blue Chrony chronograph about two months ago and have had it out to the dry lake a time or two. It gives the statistics for each of six ten-round strings-- things like high and low shot velocities, the spread between these two, average velocity, standard deviation, et cetera.

I began to wonder about statistics after I got this thing. I did a few websearches and learned that Standard Deviation is a measure of the "normalness" a sample is among the population. At least I think this is what it means. I failed my Stats class in college back in '84...

Then it occurred to me that anything that involves multiple samples could be measured for its stats. I found a website that has a standard deviation calculator and began to fool with it. You tell it how many samples you have, put in the values and hit Caculate. It will give you multiple stats on the values in just split seconds...

So last night I threw 20 powder samples on my Lee Perfect Powder Measure at a weight that is pretty much in the ballpark for my 300WSM cartridge. I arbitrarily picked about 60 grains or so of H380. I threw the charge, then weighed it on my RCBS Range Master 750 digital scale. I recorded the weights and entered them into the calculator.

For my 20 weights, the mean was 60.9 grains. The standard deviation was .250 (assumably grains). The median was 60.9 grains. The HI was 61.3 grains; the LO was 60.4 grains. Something called the "95% confidence interval for actual mean" was 60.77 thru 61.00. I think this means I have a 95% chance of throwing a charge between 60.77 and 61.0 grains, but I'm not sure. Something else called the "average absolute deviation from median" came in at .185 (assumably grains). I think this means I can expect to be .185 grains off from the median for any thrown weight. Again, I flunked Stats, so I don't know.

If anybody out there is a Stats major, I'd be gratified if you'd explain in verbiage a trucker can understand what I have in these values. I think I have a pretty repetitive measure in that the SD is just 2.5 over 609, so that's pretty good, huh? Thanks.

Get the calculator at http://www.physics.csbsju.edu/stats/cstats_NROW_form.html

I began to wonder about statistics after I got this thing. I did a few websearches and learned that Standard Deviation is a measure of the "normalness" a sample is among the population. At least I think this is what it means. I failed my Stats class in college back in '84...

Then it occurred to me that anything that involves multiple samples could be measured for its stats. I found a website that has a standard deviation calculator and began to fool with it. You tell it how many samples you have, put in the values and hit Caculate. It will give you multiple stats on the values in just split seconds...

So last night I threw 20 powder samples on my Lee Perfect Powder Measure at a weight that is pretty much in the ballpark for my 300WSM cartridge. I arbitrarily picked about 60 grains or so of H380. I threw the charge, then weighed it on my RCBS Range Master 750 digital scale. I recorded the weights and entered them into the calculator.

For my 20 weights, the mean was 60.9 grains. The standard deviation was .250 (assumably grains). The median was 60.9 grains. The HI was 61.3 grains; the LO was 60.4 grains. Something called the "95% confidence interval for actual mean" was 60.77 thru 61.00. I think this means I have a 95% chance of throwing a charge between 60.77 and 61.0 grains, but I'm not sure. Something else called the "average absolute deviation from median" came in at .185 (assumably grains). I think this means I can expect to be .185 grains off from the median for any thrown weight. Again, I flunked Stats, so I don't know.

If anybody out there is a Stats major, I'd be gratified if you'd explain in verbiage a trucker can understand what I have in these values. I think I have a pretty repetitive measure in that the SD is just 2.5 over 609, so that's pretty good, huh? Thanks.

Get the calculator at http://www.physics.csbsju.edu/stats/cstats_NROW_form.html