Home Forums Hunting & Shooting Ask The Gunwriters Foot Pound Energy

I posted this over on the Handgun Reloading Forum, but thought it might also be a good idea to post it here as well. What is the formula for calculating energy foot pounds of a load? I know it has to do with velocity and bullet weight. I would like to know how much "thump" I am getting. Thanks!

Just click on this link and fill in the blanks and it will calculate it for you:

http://www.ballistics101.com/muzzle_energy_calc.php

Excellent info. VERY useful. THANKS!

A foot pound is the amount of energy required to lift a pound by one foot.

Your 2000 foot pound load has enough energy to move a ton upward by one foot.

I use this formula.....

Bullet weight x velocity x velocity ÷ 450240

Example... 300 x 2750 x 2750 ÷ 450240 = 5038 foot pounds.

Somebody is going to ask why the 200 pound deer didn't fly ten feet.

Yup! Lousy measure of lethality. I'm glad all the really big game animals I've killed with handguns don't know that my chosen firearms don't produce enough "energy" to really kill them - haha!

Thanks Elks.

I have the equation for converting CUP to PSI - courtesy of Mr. Denton
and
the equation to determine Bore Capacity.


I have LOST & forgotten that equation. I'm putting it in My Phone Reminder Page.
Thnx

Jerry

BECAUSE the 200 lb deer BODY did not TRAP all the E. --> simple grin

Jerry

Elkster's formula.

I don't hunt cape buffalo with a Daisy Red Ryder or even a .22 LR....someplace/somewhere foot-pounds of energy does play a role in the equation. Yes, it's not everything.....but it does have a place in the scheme of things.

The food-pound theory of ballistic energy is NOT a real-world way to judge power and suitability of bullets to kill larger and large game
As an example a 22-250 with a 55 grain standard cup and core bullet has the same number of "foot pounds" of energy (1751 Ft Lbs published) as a 45-70 with a 400 grain had cast bullet (1748 Ft Lbs)
So if foot pounds were an accurate way to make comparisons we'd see the same amount of ballistic damage done by both the 22-250 and the 45-70 on a 2000 pound buffalo with a shoulder bone shot.

But we don't.

In fact the 22-250 with frangible 50 and 55 grain bullets will sometimes not exit a coyote. I know because I have killed a few hundred with 22-250 loads in my life.
I seriously doubt anyone would think a 45-70 with any 400 grain bullet could be stopped by a coyote. Cast hard, such bullet shoot clear through bull buffalo and often do it lengthwise. Yet the 45-70 has the same number of foot-pounds.

Using a different way to calculate ballistic energy that also considers diameter into the mix (diameter is what is obtuse to any bullet's direction of travel, so the larger diameter the bullet the more tissue it's striking and moving out of it's way) is to multiply diameter by weight by velocity at impact and divide by 7000 (7000 is used because we enter our weight in grains and one grain is 1/7000 of a pound)

So .224 X 55 X 3700 FPS = divided by 7000 = 6.512 We could call that 6-1/2 as a number for comparison
A 30-06 with a 150 grain bullet would be .308 X 150 X 2900 = divided by 7000 = 19.14 Lets just call this 19.
A 338 Win mag with a 250 grain bullet is .338 X 250 X 2650 = divided by 7000 = 31.23 Say... 31-1/4
A 9.3X62 with a 286 grain is .966 X 286 X 2400 = divided by 7000 = 35.88 Very close to 36
A 45-70 with a 400 grain at black powder speeds is .458 X 400 X 1275 = divided by 7000= 33.36 We could say 33-1/3
A 45-70 with the same bullet shot at 1800 FPS in a strong modern rifle .458 X 400 X 1800 = divided by 7000 = 47.10

Both the 22-250 and the 45-70 have the same number of foot pounds, but figured out this way the 45-70 with the slow black powder load has a factor of 33.3 and the 22-250 is a 6.5.

That is a whole lot closer to the real world.

The down side to this math is that all bullets would have to be of the same construction and act the same way on impact and they clearly are NOT the same, so using correct bullet for the game at hand is quite important, but that is neither here nor there when it comes to comparison ballistic power of a cartridge. That issue is more about energy use, not amount of energy in motion.

Yup, it sells ammo. I've been fighting with the establishment and conventional wisdom over the lack of terminal goodness (this is a technical term) produced by the revolvers I hunt with very publicly over articles, etc. It may be a useful tool when comparing one load to another, or it might not. A .22-250 generates (actually calculates) more energy than my .500 JRH buffalo loads yet there is no denying which is better for a large bovine.

Clearly you will not be using a BB gun or a .22 on Cape buffalo...

Elkhunters formula gets the units correct.

Bullet weight (in grains) X Velocity (in Feet per second) Squared / 450240.

Same formula works for arrows and any projectile weighed in grains and measured in Feet per Second.

Example: 2700 fps x 2700 fps x 130gr / 450,240 =2105 ft/lb

But why doesn’t it, I hit a 145lb deer with a 450 Marlin load that went in the chest and lodged in her ass, she simply fell down. It didn’t lift her at all?

Sounds like a useless figure for hunting, maybe I will ask Mr. Owl

I know from martial arts that energy can keep going even when the projectile has stopped, I’ve seen folk bust several boards but never crack board number one.

This stuff is in the rehlm of Quantum Physics

It's in another realm alright.

? Really ?

My bad, divide by 450240.

Check.