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Some Reloading Statistics
Monday, July 23, 2007 (03:42:19)
Posted by GroovyJack
Here are a few statistical numbers we arrive at when reloading and using a chronograph .. Most chronographs compute these figures for you , but they are nice to know how they are arrived at and what they mean .
For this example and to keep it brief we will use a 4 shot string instead of ten shots which gives you a much better set of numbers ..
Hv : the highest velocity recorded in the string
Lv : the lowest velocity recorded in the string
Es : Extreme Spread of the string
Av : Average velocity of the string fired
Sd : Standard Deviation , a measure of how close each shot will be to the average ...
Also I'm throwing in how to calculate ft lbs of energy and Taylor Knock Out Value , as well as number of loads per pound of powder
OK here we go with our 4 shot string
1. 2990 fps
2. 3010 fps
3. 2996 fps
4. 3004 fps
Hv = 3010
Lv = 2990
Es = 20 fps , the difference between the high and low velocities
Av = total of each velocity divided by the number of shots fired 2990+3010+2996+3004/4 or 3000fps Av
Sd is derived by multiplying the square root of the average velocity by the number of shots fired , and deduct it from the squares of all shot velocities -1 and then take the square root of this figure ..
[(2990sq+3010sq+2996sq+3004sq-4x3000sq)/(4-1)]sq= SD
54.68+54.86+54.74+54.81/3
219/3=73
73sq=8.54
Sd= 8.54 fps , or each shot will be within 8.54 fps of the average ..
FtLbs of energy is derived by the following :
velocity x velocity x bullet weight / 450240
For a 405 grain bullet at 2500 fps it will look like this
2500x2500x405/450240 = 5622 ft lbs
Taylor Knock Out Value is derived by the following formula :
bullet weight x velocity x diameter/7000
405 x 2500 x .458 / 7000
TKO of 66
Number of loads per pound of powder
There are 7000 grains in one pound of powder , so simply divide 7000 by the charge weight you are loading
Lets say you are loading 80 grains of powder in yur .17 souper mag ele slayer
7000/80 =87.5 loaded rounds per pound of powder ..
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