Muzzle energy vs Power factor?


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KJS
July 13, 2010, 04:55 AM
Looking at muzzle energy favors bullets that are lighter & faster, like a 125 gr .357 Mag.

Looking at power factor favors bullets that are heavy, even if slow.

Using a balistics chart for some ammo Remington makes:

357 Magnum: 125 gr @ 1,450 ft/sec = 583 ft-lbs of energy

45 Auto: 230 gr @ 835 ft/sec = 356 ft-lbs of energy

Based on muzzle energy the 357 is the clear winner.
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Yet I've read about power factor, so let's look at that:

375: 125 x 1,450/1,000 = 181 power factor

45 Auto: 230 x 835/1,000 = 192 power factor

So now the big slow .45 is the winner by that measure.
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Now for the question: what's the true measure?

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macadore
July 13, 2010, 06:20 AM
BMG: 700 grains x 2978 ft/sec/1000 = 2048 power factor

10 lb. Bowling ball: 70,000 grains (10 pounds) x 1 ft/sec/1000 = 7000 power factor.

Bowling ball beats them all.

KJS
July 13, 2010, 06:43 AM
Bowling ball beats them all.

Moral of the story: buy a cannon.

CDW4ME
July 13, 2010, 12:03 PM
The "power factor" is a way to compare recoil, out of comparable pistols, it's bullet weight x speed / 1,000
I chronographed two loads out of comparable pistols, Glock 19 and 23
127 +P+ out of a model 19: 1,212 fps = "power factor" of 154
180 JHP out of a model 23: 977 fps = "power factor" of 176
The 9mm kicks less.
A bullet with a greater "power factor" may or may not have more "stopping power" ;) than one with less, have to consider bullet design / FMJ v. HP.

Zotter
July 13, 2010, 12:06 PM
As I understand it - and I only slept at home last night - "Power Factor" is one of the 3 metrics used in USPSA scoring. It's not meant to be a metric of bullet performance or "efficacy" in any way.

The other 2 metrics used are time and accuracy.

The Lone Haranguer
July 13, 2010, 07:57 PM
There is little if any correlation between "power factor" and muzzle energy. Power factor is a measure of momentum, originally developed for a shooting game. Using the PF formula (bullet weight in grains, times velocity in feet per second, divided by 1,000), let's throw a couple of examples out.

.45 Auto, 230 gr. @ 850 fps: 195 power factor.
.30-06, 150 gr. @ 2,700 fps: 405 power factor.

I think everyone can agree that a .30-06 is far more than twice as powerful than a .45.

481
July 14, 2010, 12:58 AM
Now for the question: what's the true measure?

Neither.

I'd encourage you to obtain and read "Bullet Penetration" by Duncan MacPherson. Lots of perspective in that book and you'll never look at the issue of terminal ballistics the same way again.

oldfool
July 14, 2010, 01:43 AM
what macadore and Zotter said
(the reason behind your question not being very clear and/or the reason behind the endless caliber woobie wars)

KJS
July 15, 2010, 08:50 AM
A bullet with a greater "power factor" may or may not have more "stopping power" than one with less, have to consider bullet design / FMJ v. HP.

You'd also have to consider what it's hitting -- a nice soft human where a HP will make a big wound, or an angry grizzle bear that's really tough and will only be annoyed by a HP before he eats you.

Fishman777
July 15, 2010, 10:17 PM
I'm convinced that the only two things that really matter are bullet placement and penetration. You can drop just about anything, with just about any caliber, as long as you have those two things. It's not the gun or the ammo that matters, it is the shooter.

MTS840
July 16, 2010, 08:15 PM
Now for the question: what's the true measure?

This argument has gone on for decades and will go on for decades more.

As far as service caliber handguns are concerned, the true measure is how well you can shoot your chosen load from your chosen platform.

Arguing over ballistic numbers may be quite interesting, but what wins the fight is effective rounds on target.

I'd quit worrying about it and keep practicing.

Hk Dan
July 16, 2010, 11:00 PM
Here, here MYS. It's irrelevent. As long as you're shooting a service caliber handgun cartridge from a reliable and reasonably accurate gun, they have the same effect.

Fanf--if ya hit him in the forearm with a .45 he's gonna fight on. If ya hit him in the forehead with a 9mm, chances are that he won't. Reverse the story and it's still true. Shot placement--accurate shooting--that's what will provide the best "stopping power" available. Calibers? It's all window dressing.

KJS
July 17, 2010, 01:58 AM
I'd encourage you to obtain and read "Bullet Penetration" by Duncan MacPherson. Lots of perspective in that book and you'll never look at the issue of terminal ballistics the same way again.

Thanks for the suggestion. I'll have to put that on my to-do list. Once in a rare while some of those items actually get done. I'm not a big fan of books, but it sounds more interesting that the average book.

Actually, I've never looked at the issue of terminal ballistics before. About all I know is hunks of lead that are bigger & faster are more likely to kill or do severe damage (all else being equal, of course).

A full 15 years after college graduation and now I need to read a book. I thought I was long past the homework stage; guess not.

I'm quite a novice compared to most on THR and it's truly stunning how much there is to know about guns. Every time I learn more I end up knowing less, as more knowledge simply brings up further questions, and I do appreciate how all of you are willing to help out a novice who has an endless supply of basic questions.

I really wish I'd been introduced to guns 25 years ago as a kid, but I guess late is better than never.

KJS
July 17, 2010, 02:16 AM
As far as service caliber handguns are concerned, the true measure is how well you can shoot your chosen load from your chosen platform.

Yes, I fully agree with you there. I've definitely noticed that those who are the most knowledgeable about guns tend to be far more concerned with how well they can put a hole where they want a hole, rather than the size of that hole.

I've also noticed there are some macho types who hold the view that anything less than a .45 is on par with a water pistol.

Even I know a dinky .22 hole beats a 10mm round that would have produced a big hole if the shooter didn't miss. Seems the FBI back in the 1980s learned the lesson that being able to make huge holes doesn't matter if most of your agents can't handle a 10mm hand cannon and miss.

I was just curious about this power factor thing since till a few months ago I'd never even heard of it. I was just wondering what the significance of it was & why I should even care.

After the vivid example given of how a bowling ball slowly rolling ranks higher in PF than a .50 BMG, I gather it doesn't matter. I'm quite sure something that can drop an elephant with ease tops a bowling ball that might drop a few pins.

oldfool
July 17, 2010, 12:09 PM
KJS
it's a pleasure to have you on board, sir
(a little common sense every now and then never hurt any forum)

MCgunner
July 17, 2010, 12:36 PM
Power factor is momentum bases and has no bearing other than penetration potential on a soft target.

Energy as a calculation, if you must compare calculations, is more relevant, though it's by no means the end all of the argument, as far as terminal performance.

If I'm going to shoot pepper poppers or pins or something at a match, I want momentum and I'll use my .45. If I want to kill something, I'll take my .357 magnum at a minimum, leave the .45 ACP at home. If I take a .45, it'll be my Ruger Blackhawk in .45 Colt, not a .45ACP, trumps either of the other calibers big time either in power factor or energy. :D

Just pick out the right tool for the job, I say. Now, for self defense, in no way is the .45ACP inadequate, of course. :rolleyes: I carry mine now and then, but sorta prefer pocket carry, especially this time of year. I have a selection of pocket guns for that. But, I see no reason to nit pick over paper numbers when it comes to the .45 vs the .357 for defensive use. Both are among the most effective practical carry calibers on the market for this use, why they are so popular in the first place. I've killed game with the .357 and I KNOW it works on hogs and deer. I'm supremely confident in .45ACPs also, for human targets. I pay attention to proper load for the job, though. I don't carry my 180 grain load...1402 fps/785 ft lbs...for self defense, a little much in penetration I think. I own both calibers....AND a .45 Colt. :D

MCgunner
July 17, 2010, 12:44 PM
Oh, as to power factor, it is a calculation used by gamesters to even the playing field. One must "make major" (power factor) to play. Keeps recoil even, though IPSC guys in the race gun classes cheat with compensators, so I fail to see a reason for power factor unless it's a stock gun class. Power factor was not invented to judge a gun's terminal performance, but as it relates to momentum, is a momentum based calculation, it does relate to how well the gun will knock a pin off the table. Some think it relates to penetration, but there are other factors like sectional density of the bullet that matter here, and besides, either of the discussed calibers has PLENTY of penetration for self defense, especially the .357 magnum. Too heavy a bullet (higher SD as well as momentum) and the .357 is kind of inappropriate for self defense. I shoot 140s in my 3" gun at 1350 fps or there abouts.

oldfool
July 17, 2010, 01:22 PM
real well said McGunner !
great explanation of power factor

but you know you just prompted flamebacks re: 357 loads for defense (more's the pity)
me, I am good with 38+p out of 3" to 6" revolvers at/in home
(I love 357 loads out of carbines)

Route666
July 17, 2010, 08:38 PM
BMG: 700 grains x 2978 ft/sec/1000 = 2048 power factor

10 lb. Bowling ball: 70,000 grains (10 pounds) x 1 ft/sec/1000 = 7000 power factor.

Bowling ball beats them all.

I'm having trouble getting that math to work, the bowling ball works out to 70 from my maths, far below the BMG. Your point is valid though, power factor isn't a true measure of a bullet's efficacy.

Kinetic energy = 1/2 mass x velocity^2. Use the same numbers above and you will find that the BMG carries far more energy than the bowling ball under those conditions. This gives you a better indication on bullet comparison, but it doesn't take into account how quickly the energy is transfered onto the target, which is power, the rate at which energy changes in the target. Of course energy transfer without penetration would cause mostly bruising, with some hydraulic action causing bleeding, which is less lethal than penetration causing destruction and massive bleeding.

So for fairly accurate comparison power factor isn't really much good. You need power on target and wound characteristics like depth of penetration, size of hole, etc. This just happens to be what most already consider to be the way to do it.

481
July 19, 2010, 12:56 PM
A full 15 years after college graduation and now I need to read a book. I thought I was long past the homework stage; guess not.


Heh, I graduated about eight years before you (from The Ohio State University) and lemme tell ya....there is no escape from homework even at tis point. Just proves that you are younger than you think you are even if you don't want to be. :D

If you decide to try chasing the book down, it is about 5 years out of print and kind of hard to locate. (but well worth it) Might be able to provide a (hopefully still valid) link if you need it.

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