Home Forums Hunting & Shooting Ask The Gunwriters Foot Pound Energy

Might be useless, but Colorado uses it to determine the legality of hunting rifles. 1000 ft lbs at 100yards for rifles and 500 ft lbs at 50 yards for handguns.If you all think it is meaningless,try arguing with a game warden when you are using a .357 mag handgun

Just to be a nit picker......
The divisor 450,240 was change back in the late 60's or early 70's to 450,400. Apparently a group of physicists determined the results of using the earlier number didn't quite line up with some newer or more complete observations. Or so I was told a physics professor in college.
The difference in the end result, at least as far as we're concerned, is extremely small...about 1 foot pound with a 30/06 180 grain factory load.

You're Jwall.

He probably owes you a refund on at least part of your tuition. There is no one person, entity, or group who decides on the value of that constant,-- it is the combination of two other numbers, one of which is well defined and the other is pretty well defined, sorta.

Kinetic energy is 1/2 m v^2. To get it in ft-lbs, you have to divide by 7000 to convert grains to pounds, and you have to divide by the acceleration due to gravity to get from slugs to foots. Standard gravity is about 32.17405 ft/sec^2, although it actually varies from place to place.

So, 2 x 7000 x 32.17405 = 450,436.7

But, feel free to use anything close that you can remember. As noted, it doesn't change the result very much. But if you remember what the number is and why it is, then you can easily get the exact number anytime you want it.

Enjoy,

In the formula E=MC2 the "C" stands for velocity of light in meters per second. (300,000,000) and "M" is for mass in the metric system. This is difficult to apply in the English system but E=1/2KMV2.....here the "M" is for mass but the unit of mass in the English system is a slug.....or 32 pounds.

If we are to use grains and feet per second then we convert the "M" by dividing by 32 and again by 7,000 (number of grains in a pound)

because the constant "K" is 1/2 we again multiply like this.....7,000 X 32 X 2 = 448,000

Assuming a velocity of 3,000 feet per second (squared) we get 9,000,000 and times the weight of the bullet (lets assume 150 grains)
we get 3,000 X 3,000 X 150 = 1,350,000,000 Divide that by the 448,000 we get 3,013.3928 foot pounds.....check this with the 150 grain load of a .30-06

The previous number used (450,240) is likely a tad more accurate as the numbers I used are very slightly rounded but are close enough for the kind of girls I go out with.

Why Yes, I am !

How many foot lbs of energy does a 3 ounce scalpel moving 1" every minute have?

NONE, if I get my 40 out quick enuff.


just joking fellows.

Jerry

CUP and PSI are two different things and there IS NO FORMULA to convert one to the other.

Mr Denton has done a pretty fair job of estimating one in terms of the other over a short range and I congratulate him for the effort. He's fairly close....but again over a short range.

I been killin' pigs with 35 fpe? How is that possible?

Long day for me today.

"You're welcome Jwall" is what I should have wrote.

What are you using?.....

Well.....just tell Mr Denton there is no equation.
It’s not mine.


Jerry

Contender carbine, .22 short match chamber, CB shorts.

You are quite correct. The conversation with him was at his loading bench and we were discussing the various formulas for finding FPE. I mentioned that I had been using the 450240 number when he stated the more accurate formula as being 450400. He went on to explain in much greater detail on the math using, iirc, in very similar details as you mentioned and the reasoning for the change in formula which I have long since forgotten.
His final comments on the issue was to simply to round it off to 450400---it was more than close enough for the purposes at hand and that if anyone thought FPE was an accurate measure of killing/stopping power that they needed to get a hell of a lot more real world experience.

I salute you sir.....you're a better hog killer than me.....

200 lb Deer??!! Where?? Certainly not in Texas.

I lift several pounds “per foot” with every step.

-blush-

Not that tough. Cover is dense, shots very close. Little bit of camo and move like smoke is all it takes.

0.224 x 55 x 3700 / 7000 = 6.512
0.355 x 147 x 990 / 7000 = 7.380

And today I learned a subsonic 9mm load is a more effective round than a .22-250!