Some Reloading Statistics

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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

[(2990sq+3010sq+2996sq+3004sq-4x3000sq)/(4-1)]sq=SD

54.68+54.86+54.74+54.81/3

219/3=73

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

Class Dismissed 

Comments

GooseHunter Jr's picture

That is alot of great

That is alot of great info..almost so much info there that my head almot exploded.  Thanks for all the info and I hope I willbe able to put it to get use.

Deer Slayer's picture

I don't think I will ever use

I don't think I will ever use these numbers but thanks for the information in case I do. If you don't mind me asking, do you know all these numbers because you are some type of sniper or something?

groovy mike's picture

Thanks for the lesson Jack.

Thanks for the lesson Jack.  Now we just need to translate all that math into something that we can understand.  Loads per pounds I understand, but Taylor Knock Out Value and foot pounds of energy are equally useless to me since they don’t mean anything until I have something to compare them against.  I think what we need is a baseline – like a standard 308 load to compare to and then readers can figure out if their favorite cartridge is more or less potent than a known quantity.  We all know that a 30-30 has less oomph than a 308 and a 30-06 has more.  But how much in each direction is the question?  Then once we have a baseline we can start comparing things like 300 Win mag and 338 to decide which is “better” ;)

ManOfTheFall's picture

Thanks for the tip. I

Thanks for the tip. I probably won't ever use this but in case I do I will now have a place to reference off of.

hunter25's picture

I have mentioned that I do

I have mentioned that I do plan to get back into reloading soon as I have everything that I need it's just been put away for a few years. But when I say need it does not include a chronograph. Although not needed it does add a a whole new level of information that can be used to narrow a good load down faster. And of course it's good to see just how that velocity compares to all those numbers that are published in manuals and on the backs of boxes.

Thanks for the primer now I want one of those also.

jaybe's picture

Thank you, professor Jack.

Thank you, professor Jack. That's some pretty interesting stuff there. I can see that you get into the finer details of reloading much more deeply than I do - probably more than most.

I use the figures that are published by either the bullet maker of the powder maker to figure out what the exterior ballistics are and go with that. The numbers that I am interested in are the trajectory of the bullet, so I will know what my bullet drop will be at different ranges. Beyond that, I'll load the bullet I have chosen for the particular animal to the highest velocity that my rifle will accurately shoot. I guess I just leave the energy or TKO numbers to fall where they may. I figure if I can get a well-constructed bullet to the animal's vitals, I've done my part.

Thanks for the details, though. It makes interesting reading and also may encourage others to get more involved in reloading. It really adds another dimension to hunting when you take an animal with a load that you have put together.

 

ndemiter's picture

so i set up a dimensional

so i set up a dimensional analysis worksheet for myself on the TKO equation. i can't for the life of me figure out why you would devide the product of all those numbers. i guess it's like deviding your number of oranges by a tangerine.

but, if you just allow the "7000" to represent any constant, you can get a comparison of relative power between two rounds of the same diameter.

not bad info though. plus i enjoyed the unit analysis. i guess i'm kind of a freak that way.