Figuring Energy


March 21, 2003, 04:50 PM
Got the latest American Rifleman today and in it is the formula for figuring ft/lbs of force for a given projectile weight and fps. Thought I'd go ahead and post it and figure the Ft/lbs on one of those 5"/54's we was talkin about a while back
here goes...

KE = (W x V squared) /450,400

KE=Kinetic Energy (ft/lbs)
W= weight of bullet (grains)
V= Velocity (fps)

so that gives us:

72 lbs x 7000 = 504000 gr

KE = (504,000gr x 2600 fps sqd) / 450,400

KE = (504,000 x 6,760,000) / 450,400

KE =3407040000000 / 450400

KE = 7,564,476.02 ft/lbs

imagine that,,,now thats a wallop


and whats a .357?


KE = (158 gr x 1300fps sqd) / 450,400

KE = (158 x 1,690,000) / 450,400

KE = 267,020,000 / 450,400

592.85 ft/lbs

this works...

one more...

KE = (85 gr x 1o00 fps sqd) / 450,400

KE = (85 x 1,000,000) / 450,400

KE = 850,000,000 / 450,400

KE = 188.72

it works!! it works!!

oh well, thought it might be of interest or use to some of us



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March 21, 2003, 06:17 PM
Ah, metric units are so much easier, no silly factors needed: :D

8 gram bullet at 400 m/s: 0.008kg / 2 * (400m/s)² = 640 kgm²/s² = 640 Joules

Oh, actually it should be lbs*ft, not lbs/ft, as force * distance = energy, force per distance is a distributed type of load. ;)

March 21, 2003, 06:19 PM
The problem is that 'energy' has little to do with it. What you need to do is penetrate into the vital organs and disrupt those organs. So velocity, caliber, weight , bullet construction are all more important than energy. It's one of the great myths of bullet performance.

March 21, 2003, 06:30 PM
checking back with the magazine (the paper one) i see that they actually record this measurement as ft - lbs but i'll take your word for it...

i'm just glad i can plug and chug through the formula...

shows i got something out of those 8 years of college...

:p your opinion, mete, what would be the "perfect round" for self defense?


March 21, 2003, 07:01 PM
Thanks I was just trying to determine the energy of a black powder pistol round to see if it qualified for deer hunting.

March 21, 2003, 07:05 PM
Or you can use the Online Muzzle Energy Calculator (! Kinetic energy is the ONLY, and I mean, ONLY scientific measure of how powerful a round fired actually is. It's been said that velocity, bullet weight, and other things are more important. Well, more velocity and more bullet weight give you more kinetic energy.

March 21, 2003, 07:05 PM
Coonans formula for muzzle energy = Bang+splat =food :D

March 21, 2003, 08:50 PM
280's revised formula for coonan: bang + splat = what time is supper?


March 22, 2003, 03:11 AM
shhh!!!!! I am sneaking up on a herd of deep dish pizzas :D

March 22, 2003, 06:50 AM
hit that sausage, mushroom and onion one over on the left there at about 200 yards......


March 22, 2003, 08:04 AM
280plus, I don't like the numbers game in any way whether it's KE or % one shot stops because the real world is a bit different. Of the reasonable defense cartridges by far the most important is bullet placement. So pick a gun that you can shoot well and practice and get proper training. From all my research on the subject there isn't any difference on the street between 357sig, 40, 45, or 357 and the 9mm is close to them .Use premium bullets.

March 22, 2003, 10:20 AM
200 yards you have to be crazy anyways thats one of them thincrusts , thers a deepdish out a 300 . hope you like extra cheese!!! bang!!!!! thwap. ( pizza sauce flying everywhere easier to track that way .....) uh dude I think a 8mm is just a little to much of a heavy hitter... :D

March 22, 2003, 03:39 PM
deep dish it is...

I'll go see how much is left of it...


well mete, i'm ccw with a j frame s&w lightweight .32 mag and assuming the pelvic and abdominal areas are the right place for deposit with these.

my job makes it hard to carry anything much bigger, lots of ladders and tight places.


March 22, 2003, 03:57 PM
280plus, you need to do a bit of research on the subject. Pelvic/abdomin is not the place for stops. There was an interesting police video - a cop shot a bad guy in the abdomin with a 45 , you could hear him saying that he thought a 45 would have more effect, it was a poor location to hit and it had almost no effect. Hits should be above diaphram ( heart /lug area ). As for a gun a small 9mm such as a Kahr would be no larger than a J frame and somewhat slimmer.

March 22, 2003, 09:19 PM
but not hear...

See, this is something i was told by a local "been through all the police defense courses" guy, why, he even had to shoot a cow between the eyes to graduate from one of them, so he said.

the pelvis is supposed to be the key, "take out the tracks and the tank can't move anymore."

I've seen the small kahrs but i feel better with a revolver so if worse comes to worse i'll bite the recoil bullet (no pun intended) and step up to the airlite .357. for ccw and not a lot of shooting. just the figures above tell the tale. I'm sure I'll be able to find a barely used one with little problem.

I did find that the .32 mag 85 gr pushed to 1100 fps generates 228 ft-lbs., slightly better than the average .38 spec.,

As ive said here in the past, the .32's extra shot and controllable recoil are what sold me on this pistol. i'll bet i can release at least 3 ACCURATE shots in the same time it'll take a .45 or .357 in the hands of an average shooter to release two, its that fast.

hopefully i'll never have to put all this to the test


This reminds me, you must have seen the clip where a police officer was fired upon as he approached a vehicle he had stopped. If you recall his first round of return fire hit the driver's side mirror and then his second round hit the ground at about the rear tire of the subject vehicle. He was unable to recover and deliver that second shot accurately. He didn't get off a third. The driver, I believe, got away. The officer had at least a 9mm if not a .45, to me, thats what it's all about shots #2,3,4 etc. how good ya gonna be able to get those ones off?


March 22, 2003, 10:28 PM
it should be mass not weight.

Chuck Dye
March 22, 2003, 11:04 PM

lbs. weight/32.17=slugs mass, the conversion from weight to mass is included in the 450,400.

March 23, 2003, 03:14 AM
my mistake I overlooked that part. I guess I should read more carefully before I open my big mouth. :o

March 23, 2003, 05:54 AM
280plus, please tell me that you are not so naive as to believe that " he had to kill a cow" to pass the course. Read some books by reputable instructors - Farnam, Ayoob etc.

March 23, 2003, 06:38 AM
heh, heh, now, while being naive would not be one of my stronger traits, i'll tell you we're talking about one of our local range officers here, retired army.

he claims that both he and his wife took this high level police style course, (level 5 he called it, or something similar) and i think it was supposed to be in new hampshire, and the "final exam" if you will was to go to the local meat packing plant and he offed a cow and she a pig by blasting them between the eyes with their main carry weapons to:

A. prove they could actually look into its eyes and do it.
B. see what it feels like to kill
C. they then dissected the heads to study the damage.

Ive met them both and they seem like otherwise normal people, if there is such a thing...

now the question is: Fact? or "the silliest thing you've ever heard in a gun discussion"

just for ha-has i told him i would have trouble killing an innocent cow but if that cow was trying to molest me or my family...


oh, i have read a little on the subject, and one military style series i have read recommends that the belt buckle be your target, why? it gives you an equal chance for a hit in terms of elevation, if you shoot too high or too low in your excitement, this will increase your chances for a hit. anyhow, i'll look into these other authors cause you can never be too smart when it comes to this stuff...


March 23, 2003, 08:01 AM
280plus, I've only shot 4 legged things, but many of those. I've never gut shot a deer but those deer are usually lost even with rifles. That's why they say for deer heart, lungs, or spine.

March 23, 2003, 02:34 PM
deer wouldn't have so much trouble if they weren't so tasty...

so far the only thing i ever "offed " in my life was a poor unfortunate rabbit that fell across the sights of my bb gun when i was around 12, i still feel guilty about it


though hunting is becoming more attractive to me as i get older

them turkeys i see runnin' around look mighty darn tasty too!

and besides, they're so darn arrogant...


without dwelling on the subject much longer, when you're shooting low, your target IS the spine. gruesome i know but this is in response to being attacked.

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