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I wouldn't personally put much stock in the "efficacy" number it calculates.

For determining muzzle energy, there is a very quick and easy to remember formula that is usually within a couple tenths of a percent of the proper (and much more complicated) equation.

bullet weight (in grains) divided by 100

times

muzzle velocity (in fps) divided by 100

times

muzzle velocity (in fps) divided by 100

times

2.22

Or in simpler terms:

(weight / 100) * (velocity / 100) * (velocity / 100) * 2.22

So a 230gr round at 850 is: 2.30 * 8.5 * 8.5 * 2.22 = 368.908
The normally reported ME for a 230gr .45 at 850 is 369 ft-lbs.
 

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Discussion Starter · #3 ·
Thanks, Todd!

Nice to have the math behind the calculations. But, for most of us, it's very handy to have an online calculator for such things - especially when we have a number of rounds/caliber/gr. weights to play around with.

Regarding efficacy - these things can get a little subjective for sure. Hence, the ongoing debate concerning the efficacy of a high speed 9mm vs. a relatively slow speed 45, for instance. No doubt that the creator of this calculator comes down on one side rather than the other.

For sure, we all need to take into consideration such things as expansion, penetration, and the ultimate integrity of projectiles at the speeds our own carry gun is able to provide.

Regardless of the method/figures used - most will agree that frontal area of the projectile has "something" to do with it's effectivness in stopping the assault of a human assailant.

Witness the fact that the weapon of choice of dangerous big game guides is often a 12 guage shotgun with slugs or (applied at the last second of a charge) 00 buck that has expanded in patern no more than the size of a human hand.

It's proven effectivness in stopping the assault of dangerous soft skined game is legendary and without dispute. That effectiveness goes far beyond the mere paper energy of the round in question. The paper energy of a deer rifle often goes far beyond that of a 12 guage with slugs of buckshot.

But I know of no big game guide who would rely on their favorite deer rifle to stop the charge of a lion or leapard at common pistol fighting ranges.

But the purpose of the post was not to argue his effacacy conclusions via a formula. It was to provide a very handy tool for ammo selection thoughts and for playing around with such concepts in general.
 

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The actual math is a bit more complicated. The "2.22 rule" is just a good shorthand.

Energy is mass times velocity squared. (E=mv^2)

We measure bullet weight in grains and velocity in feet per second, but the U.S. standard measurement for ammunition muzzle energy is measured in foot-pounds. So, some conversion is necessary.

The generally accepted modern calculation is:

mass (in grains) x velocity (in fps) x velocity (in fps)
-------------------------------------------------------------- = muzzle energy
450,400

In older books and loading manuals you might see the number 450,240 used instead. Back then, 32.16 ft/sec^2 was thought to be the acceleration of gravity, but today the generally accepted number is 32.174 ft/sec^2 (9.81 m/sec^2 actually).

Once you account for significant figures, it's all a wash:

100gr projectile at 1,000fps:

2.22 rule: 1 * 10 * 10 * 2.22: 222 ft-lbs

old equation: 100 * 1000 * 1000 / 450240 = 222.1037 (222 after sig figs)

new equation: 100 * 1000 * 1000 / 450400 = 222.0249 (222 after sig figs)

That's why once in a while you'll see different manufacturers have slightly different numbers for cartridges with identical weight & velocity. They're just using slightly different calculations and if a particular load is very close to being rounded up or down to the next whole number you can make just enough difference to skew things.
 

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Hey Todd...
I'll bet you were really good at those old ones like.... If a train leaves point A traveling 45 miles an hour and a plane leaves point B traveling........You get the idea.....

See, I am a brat.....
SK
 

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Discussion Starter · #6 ·
I always knew that the online calculator was pretty handy to have.

But I never dreamed........................
 

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Is this that new math, I keep hearing about ;D ;D
 

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ToddG - Kinetic Energy is actualy 1/2(mass)(velocity squared). Your formula is off by a factor of 2X.

Potential energy, which doesn't really come into play here, is (mass)(velocity)(height).

Bill
 

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ive always used this formula....velocity squared times bullet weight in grains divided by a constant of 450436.

V2 x W(gr.) divided by 450436.

850fps x 850fps = 722500 x 230gr. = 166175000 dived by 450436 = 368.92~ Ft. Lbs of kenetic energy for a standard .45acp round....
 

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Alrighty there Clark....not sure what that even means. ;)

I am glad to see the calculators though, it helps the average Joe like me (or average Brian) to get a better idea of the "power" behind different calibers. Thanks guys.
 

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Buckeye Fan said:
Alrighty there Clark....not sure what that even means. ;)

I am glad to see the calculators though, it helps the average Joe like me (or average Brian) to get a better idea of the "power" behind different calibers. Thanks guys.
What's that?

If I had a post I can't see it.

I know I have an LCP with laser in my pocket.
 

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I don't remember where I got it from, maybe from Guns and Ammo Magazine article quite some time ago, but I wrote it on the top of my loading bench for future reference and hear it is:
weight / 100, times velocity / 100, times velocity / 100, times 2.22 = _______

I think this is the same as some of you found, it is close but not exact, therefore only an estimate.
 

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Pictures worth a thousand formulae: (nothing about smaller than 9 mm though)

 
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