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Muzzle Energy Ft Lbs - Important?
- Thread starter Old cop
- Start date
USAF385
US Veteran
Ft lbs is the energy of the bullet. It's derived from the velocity and the weight (which you mentioned).
What good is a 158 gr bullet traveling at 300 ft per second? It only has 32 ft lbs of energy. The energy behind a bullet is what allows it to do damage to a target. Not enough ft lbs = not enough result.
Off topic: here's a cool fact....
A projectile moving at 671 ft/sec will have energy in ft lbs equal to its weight in grains.
What good is a 158 gr bullet traveling at 300 ft per second? It only has 32 ft lbs of energy. The energy behind a bullet is what allows it to do damage to a target. Not enough ft lbs = not enough result.
Off topic: here's a cool fact....
A projectile moving at 671 ft/sec will have energy in ft lbs equal to its weight in grains.
venomballistics
Well-known member
energy is a function of mass * velocity squared.
essentially you can think of it as a bank account to be spent on weight and penetration, or speed and terminal upset or any point in between
essentially you can think of it as a bank account to be spent on weight and penetration, or speed and terminal upset or any point in between
USAF385
US Veteran
If you want to figure ft lbs yourself, an easy way to find it is:
Take the weight in grains times the square of the velocity and divide that number by 450240. (A constant created by multiplying two times the acceleration of gravity (32.16 fps) by 7,000 (number of grains in a pound)). I won't go into depth on why it works, but it does.
Example:
158 grains at 850 fps
(158x850x850)/450240=254 ft lbs
Take the weight in grains times the square of the velocity and divide that number by 450240. (A constant created by multiplying two times the acceleration of gravity (32.16 fps) by 7,000 (number of grains in a pound)). I won't go into depth on why it works, but it does.
Example:
158 grains at 850 fps
(158x850x850)/450240=254 ft lbs
cussedemgun
Well-known member
The long story, or the condensed version?
We could go into a lengthy discussion of internal ballistics, external ballistics & terminal ballistics as they each relate to the energy calculations, BUT - -
The short version;
heavy bullet, greater bullet drop at longer range BUT better penetration at moderate range.
light bullet, great velocity/trajectory but lacking the deep penetration of the heavies upon impact.
For me & mine, no matter how the marketing hype tends to lean, I will stick with what works, before trusting my defenses to new advertising "energy" figures.
After all you already said it, "because I know from experience it works on the street".
We could go into a lengthy discussion of internal ballistics, external ballistics & terminal ballistics as they each relate to the energy calculations, BUT - -
The short version;
heavy bullet, greater bullet drop at longer range BUT better penetration at moderate range.
light bullet, great velocity/trajectory but lacking the deep penetration of the heavies upon impact.
For me & mine, no matter how the marketing hype tends to lean, I will stick with what works, before trusting my defenses to new advertising "energy" figures.
After all you already said it, "because I know from experience it works on the street".
David R
Well-known member
A bullet traveling at 950 fps has double its weight in grains in Foot pounds.
Velocity (fps) x Velocity (fps) x bullet weight in grains divided by 450240 = energy in ft lbs.
For example. YOUR 158 grain bullet traveling at 900 fps.
900x900 = 810000
810000 x 158 = 127980000
127980000/450240 = 284 Ft lbs.
Now lets take MY 158 grain @ AV 950 fps.
950 x 950 = 902500
902500 x 158 = 142595000
142595000/450240 = 316 ft lbs.
This is when a chrony is a good thing.
For one more, MY 110 JHP @ 1100 fps
1100 x 1100 =1210000
1210000 x 110 = 133100000
133100000/450240 = 295 ft lbs energy
David
Velocity (fps) x Velocity (fps) x bullet weight in grains divided by 450240 = energy in ft lbs.
For example. YOUR 158 grain bullet traveling at 900 fps.
900x900 = 810000
810000 x 158 = 127980000
127980000/450240 = 284 Ft lbs.
Now lets take MY 158 grain @ AV 950 fps.
950 x 950 = 902500
902500 x 158 = 142595000
142595000/450240 = 316 ft lbs.
This is when a chrony is a good thing.
For one more, MY 110 JHP @ 1100 fps
1100 x 1100 =1210000
1210000 x 110 = 133100000
133100000/450240 = 295 ft lbs energy
David
A few things....
As far as SD goes muzzle energy is important, but shot placement is primary.
a quick equation:
Energy ft-lb = (v2 + Wt grains)/450,400
In pistols 500 ft/lb seems to be a gateway to one stop shots, but again, that depends on placement, Proper penetration and bullet performance. There must be something to the 500 ft-lb number because many LEOs moved from the .38 to the .357 which is capable of producing that enery.
Hitting a target in the 'center of mass' increases likelyhood of a quick stop by piecing important nerve centers, such as the spine (or the brain if you're confident with head shots) that will drop a vertebrate instantly.
Targets have been stopped in their tracks with far less than 500 ft-lbs. A good shot with a .22 is better than a miss with a .44 magnum.
As far as SD goes muzzle energy is important, but shot placement is primary.
a quick equation:
Energy ft-lb = (v2 + Wt grains)/450,400
In pistols 500 ft/lb seems to be a gateway to one stop shots, but again, that depends on placement, Proper penetration and bullet performance. There must be something to the 500 ft-lb number because many LEOs moved from the .38 to the .357 which is capable of producing that enery.
Hitting a target in the 'center of mass' increases likelyhood of a quick stop by piecing important nerve centers, such as the spine (or the brain if you're confident with head shots) that will drop a vertebrate instantly.
Targets have been stopped in their tracks with far less than 500 ft-lbs. A good shot with a .22 is better than a miss with a .44 magnum.
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Bkreutz
US Veteran
Looks too much like math for me to get involved in this conversation. 
Badquaker
Well-known member
ballistics
Here is a primer. It's like rocket science.
I believe that what you are really looking for is terminal ballistics (how a bullet transfers energy and creates wounds). It's not all about power, bullet performance plays a big roll. People have died from being shot with a BB gun, it's just not as efficient as a 50bmg.
Here is a primer. It's like rocket science.
I believe that what you are really looking for is terminal ballistics (how a bullet transfers energy and creates wounds). It's not all about power, bullet performance plays a big roll. People have died from being shot with a BB gun, it's just not as efficient as a 50bmg.
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BigBill
Absent Comrade
Shot placemnt is very important.
I seen a guy in the ER that was gut shot five times with a 1911/45acp and live.
I over heard a doctor in the ER say he hasn't seen wounds this bad since nam. When the 10mm pistols hit the streets.
I seen a guy in the ER that was gut shot five times with a 1911/45acp and live.
I over heard a doctor in the ER say he hasn't seen wounds this bad since nam. When the 10mm pistols hit the streets.
5-Shot
Well-known member
Energy is the "ability to do work". Roughly, it is a rounds ability to create a wound volume. Think of if as potential. As others have already stated other factors such as shot placement bullet weight and design are equally (perhaps more) important. An ultra high velocity varmint rifle shooting a frangible bullet might have enough energy to kill a deer but if that energy is expended creating a surface blowout, it isn't going to work. On the other hand a 458 WM shooting solids isn't going to be great on dear either because most of the energy will be wasted on the countryside beyond the deer. Conversely, insufficient energy is insufficient...Period.
This has been a subject of heated (near religious) debate for generations among riflemen.
Ed
This has been a subject of heated (near religious) debate for generations among riflemen.
Ed
UncaGrunny
US Veteran
Muzzle energy is not a good indicator of fight-stopping ability. What counts is usually a certain amount of penetration, and the shooter's ability or blind luck to hit an organ that the perp can't fight well without. Also, sometimes the perp just doesn't like being shot, and quits on his own, more or less unrelated to the actual physical damage done. Nice when it happens, but nothing to count on. The original poster listed a cartridge well known to have adequate penetration and sometimes expansion. [Expansion, of course, is a good thing as long as it doesn't reduce penetration below an acceptable level.] The FBI load is probably one of the best .38 Spl defense cartridges. Maybe it is the best.
safearm
US Veteran
Actually, it's closer to 400 ft/lbs. If you look at all of the "modern" self-defense/LE duty ammo, it ranges in the mid-400s. For example, the "King of the Hill," .357 Magnum 125 grain JHP at 1250 ft/sec generates approximately 434 ft/lbs.
I once asked if Evan Marshall, the author of a number of books on Stopping Power and retired Detroit detective, if there was any scientific/physiological basis to the 400 ft/lbs minimum for SD, and he said (I'm paraphrasing the conversation) he wasn't aware of any, other than street results indicate that rounds with less than 400 ft/lbs of muzzle energy don't do as well. He also said the opposite is true, that rounds with over 500 ft/lbs become less controllable without any advantage of stopping power.
That's it in a nutshell.
Rastoff
US Veteran
Actually, it has no importance. It's simply the other numbers, bullet mass and feet per second at the muzzle, manipulated to give a value that can be used for marketing.
What's important, as alluded to earlier, is terminal energy. This is the number that demonstrates how much energy is available to transfer to the target when the bullet gets there. Because there is no set distance for that, it cannot be put on a box. So, they use the values calculated at the muzzle because they are consistent.
Or are they? A round that has 424ft/lbs of energy at the muzzle of a 5" gun won't have that same value at the muzzle of a 3" gun.
Yes, it really is rocket science and this is all I'm going to add here.
ft/lb is nice to have but.......................
Bullet placement
penetration depth
bullet expansion %
amount of damaged tissue
wound channel
mental & physical condition of target
and exits..........
all play a part..........Go ahead, pick a card.
Bullet placement
penetration depth
bullet expansion %
amount of damaged tissue
wound channel
mental & physical condition of target
and exits..........
all play a part..........Go ahead, pick a card.
I'm sure my info is old.....
I'm sure my info is old here. Improvements in bullet performance has changed the game a little.
I'm sure my info is old here. Improvements in bullet performance has changed the game a little.
BigBill
Absent Comrade
If I remember correctly my loads for my 357/125gr bullets were 1,500fps.
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