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 four shot string instead of ten shots which gives you a much better set of numbers.
Also I'm throwing in free :
how to calculate foot pounds of energy
Taylor Knock Out Value
as well as number of loads per pound of powder
Hv: the highest velocity recorded in the string
Lv : the lowest velocity recorded in the string
Es : extreme spread of the string ( the difference between the highest and lowest velocity in fps )
Av : average velocity of the string fired
Sd : standard deviation , a measure of how close each shot will be to the average
OK here we go with our four shot string
1. 2990 fps
2. 3010 fps
3. 2996 fps
4. 3004 fps
Hv : 3010 fps
Lv : 2990 fps
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 3000 fps average velocity
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
73sq= 8.54fps , or each shot will be within 8.54fps of the average
On to the free stuff :
foot pounds of energy ( which to me is a totally worthless figure and means nothing . another story alltogether )
velocity x velocity x bullet weight/450240
for a 405 grain bullet at 2500 fps it will look like this :
2500 x 2500 x 405/450240 = 5622 ft lbs
Taylor Knock Out Value was derived by one of my dead heros John "Pondoro" Taylor , this value was originally used for solids and the arithmetic is for solids , but many use it to compare softs as well , with either softs or solids , to me , it is a better guide ..
As with foot pounds , TKO has guide numbers for various critters ..
bullet weight x velocity x diameter/7000
again we use the 405 grain .458 diameter bullet at 2500 fps
405 x 2500 x .458/7000
TKO of 66
Number of loads per pound of powder .. This is very basic but many people do not know how many grains are in one pound ..
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 your .17 souper mag ele slayer
7000/80= 87.5 loaded rounds per pound of powder