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Old 01-11-2019, 10:41 AM   #1
Txsurveyor2014
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Default Energy vs Velocity

I asked a question on another thread, mainly because I am still trying to wrap my pea brain around the subject and ballistics are intriguing.

Everyone has seen numbers quoted to kill a specific game animal in regards to energy, such as 800 ftlbs for whitetail, 1000 for elk, etc., but how were those numbers scientifically derived? Bullet manufacturers state minimum velocity for the bullet to perform as designed.

So which is more important, velocity at impact and bullet design or energy at impact?
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Old 01-11-2019, 10:52 AM   #2
diamond10x
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I would say energy then bullet design and velocity. I say energy first because without enough energy you cannot get any penetration no matter what the bullet design is or how fast it’s going.
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Old 01-11-2019, 11:02 AM   #3
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Bullet construction and energy. I can shoot a deer with a 35 grain frangible bullet from a 22-250 going roughly 4000 fps with poor results. That's smoking fast, but if it his bone it's ineffective and explode (perfect for p-dogs!). You can shoot a 400 grain bullet out of a 45-70 at 1800 fps for about the same energy, but it will go through just about anything.
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Old 01-11-2019, 11:07 AM   #4
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Quote:
Originally Posted by Jared.King View Post
Bullet construction and energy. I can shoot a deer with a 35 grain frangible bullet from a 22-250 going roughly 4000 fps with poor results. That's smoking fast, but if it his bone it's ineffective and explode (perfect for p-dogs!). You can shoot a 400 grain bullet out of a 45-70 at 1800 fps for about the same energy, but it will go through just about anything.
I agree with you, which is what I am confused about. What if the 35 grain bullet was designed for bigger game? For instance, if the bullet was designed to penetrate 2 or 3 inches and then mushroom with near 100% weight retention at those speeds.
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Old 01-11-2019, 11:08 AM   #5
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Originally Posted by Jared.King View Post
Bullet construction and energy. I can shoot a deer with a 35 grain frangible bullet from a 22-250 going roughly 4000 fps with poor results. That's smoking fast, but if it his bone it's ineffective and explode (perfect for p-dogs!). You can shoot a 400 grain bullet out of a 45-70 at 1800 fps for about the same energy, but it will go through just about anything.
Good answer ! I shot a big boar once behind the shoulder with a 40 gr. 22-250 bullet. At 200 yards it was still moving plenty fast, but the hog faltered, then ran toward me. Another between the eyes at about 100 yards ended that. A 150 grain bullet traveling at 1,000 fps less and it would have been one and done.
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Old 01-11-2019, 11:08 AM   #6
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I have no idea how those energy numbers were originally derived.

The rest IME depends, with the right bullet or arrow an animal can be killed with very little energy. However the drt kills that don't hit the CNS are generally from guns that have higher energy and velocity. Basically to to kill whatever, you need at a minimum enough momentum to drive a projectile into a vital area. All the rest seems to be based on a persons experience amd what they are trying to accomplish.

Hopefully that response makes some sense
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Old 01-11-2019, 11:10 AM   #7
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Originally Posted by RJH1 View Post
I have no idea how those energy numbers were originally derived.

The rest IME depends, with the right bullet or arrow an animal can be killed with very little energy. However the drt kills that don't hit the CNS are generally from guns that have higher energy and velocity. Basically to to kill whatever, you need at a minimum enough momentum to drive a projectile into a vital area. All the rest seems to be based on a persons experience amd what they are trying to accomplish.

Hopefully that response makes some sense
This is exactly what I am referring to.
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Old 01-11-2019, 11:11 AM   #8
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I like to examine momentum and bullet design personally. Ultimately, it's the time rate change of momentum that's important but that is very difficult to evaluate beyond just looking at bullet design.

I personally am more comfortable with a medium weight bullet going reasonably fast rather than a light/fast or heavy/slow bullet.
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Old 01-11-2019, 11:12 AM   #9
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E=mv

It all works together.
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Old 01-11-2019, 11:14 AM   #10
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I think energy and momentum are being used as the same meaning. Mass x Velocity = Momentum.

A freight train going 30 mph will have more momentum than a F150 going 70 mph. Takes longer for the train to get rid of all its velocity because its heavier.
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Old 01-11-2019, 11:17 AM   #11
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Quote:
Originally Posted by Txsurveyor2014 View Post
I agree with you, which is what I am confused about. What if the 35 grain bullet was designed for bigger game? For instance, if the bullet was designed to penetrate 2 or 3 inches and then mushroom with near 100% weight retention at those speeds.
I don't think it would work because there isn't enough mass for adequate momentum. There's no sectional density, and that combined with a poor ballistic coefficient spells trouble. Go look at a ballistic chart and see how fast the energy and velocity drops. It would still have poor penetration.
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Old 01-11-2019, 11:23 AM   #12
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Originally Posted by Radar View Post
I think energy and momentum are being used as the same meaning. Mass x Velocity = Momentum.

A freight train going 30 mph will have more momentum than a F150 going 70 mph. Takes longer for the train to get rid of all its velocity because its heavier.
When i use the terms i am not using them interchangeably. Energy rewards speed because it squares velocity, momentum tends to reward weight. An example is my recurve with 720 grain arrows at 180 fps has the as much momentum as some 9mm ammo, but has nowhere near the energy. The recurve will out penetrate the 9 substantially however and is considered plenty for elk or moose, but not many people would take a 9 for that
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Old 01-11-2019, 11:27 AM   #13
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Quote:
Originally Posted by Radar View Post
I think energy and momentum are being used as the same meaning. Mass x Velocity = Momentum.

A freight train going 30 mph will have more momentum than a F150 going 70 mph. Takes longer for the train to get rid of all its velocity because its heavier.
I think we are on the same page, but I am trying to figure out where the specific number required to kill comes from. Google just comes up with opinion, not facts for me.

Example: You need 800 fpe to kill a deer. So a hunter shoots a deer at way too extended range, and it is a bang/flop drt, but then calculates the energy at impact and it was only 760 fpe. Or hunter shoots an animal at close range and the bullet disintegrates because it wasnt designed for impact at such a high velocity, and even though the energy exceeds the stated requirement, the deer runs and suffers. Both cases contradict what we go by on required energy. Which is why I am asking, is bullet design and velocity more important than energy? (And honestly not trying to argue with you...lol)
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Old 01-11-2019, 11:29 AM   #14
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Quote:
Originally Posted by RJH1 View Post
When i use the terms i am not using them interchangeably. Energy rewards speed because it squares velocity, momentum tends to reward weight. An example is my recurve with 720 grain arrows at 180 fps has the as much momentum as some 9mm ammo, but has nowhere near the energy. The recurve will out penetrate the 9 substantially however and is considered plenty for elk or moose, but not many people would take a 9 for that
Yes.
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Old 01-11-2019, 11:32 AM   #15
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I think it gets into energy and mass required to get "x" inches of penetration. The further you need the bullet to penetrate the more mass you need. A 22-250, 270, and 300 can all hit at the same energy, but bullet penetration and transfer of energy will be vastly different.
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Old 01-11-2019, 11:36 AM   #16
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As they say, there's no replacement for displacement.

What we're really talking about is producing wound channels that have the depth and shockwave needed to near-instantly kill the animal we're hunting with a minimum of wasted meat.

Energy is the most common unit for measuring this, but is not the same thing as a "unit of wound generation, depth and shockwave". The difference is most apparent when talking about bullet caliber, where for a given amount of energy and the same bullet construction, they tend to produce larger wound channels. Which is pretty intuitive - bigger bullets make bigger holes, and bigger holes are more lethal than small ones.

Often people bring up archery in these discussions, and they should not. Arrows kill by laceration, not by creating shockwave wound channels.
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Old 01-11-2019, 11:42 AM   #17
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energy=0.5*m*v^2. where m=mass and v=velocity. you see that doubling your velocity will give you 4x the energy but doubling mass only gives you 2x. to me velocity is important but shot placement is king. since velocity and energy at impact are nearly one and the same and that's something you would calculate. but bullet design is important for what game you plan on taking regarding penetration.
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Old 01-11-2019, 11:48 AM   #18
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Quote:
Originally Posted by Balcones_Walker View Post
As they say, there's no replacement for displacement.

What we're really talking about is producing wound channels that have the depth and shockwave needed to near-instantly kill the animal we're hunting with a minimum of wasted meat.

Energy is the most common unit for measuring this, but is not the same thing as a "unit of wound generation, depth and shockwave". The difference is most apparent when talking about bullet caliber, where for a given amount of energy and the same bullet construction, they tend to produce larger wound channels. Which is pretty intuitive - bigger bullets make bigger holes, and bigger holes are more lethal than small ones.

Often people bring up archery in these discussions, and they should not. Arrows kill by laceration, not by creating shockwave wound channels.
This last sentence is spot on, although there must be some attention paid to energy of the arrow to get enough penetration to reach the vitals. But yes arrow energy and bullet energy are 2 different things IMHO.
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Old 01-11-2019, 11:48 AM   #19
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Quote:
Originally Posted by Txsurveyor2014 View Post
I think we are on the same page, but I am trying to figure out where the specific number required to kill comes from. Google just comes up with opinion, not facts for me.

Example: You need 800 fpe to kill a deer. So a hunter shoots a deer at way too extended range, and it is a bang/flop drt, but then calculates the energy at impact and it was only 760 fpe. Or hunter shoots an animal at close range and the bullet disintegrates because it wasnt designed for impact at such a high velocity, and even though the energy exceeds the stated requirement, the deer runs and suffers. Both cases contradict what we go by on required energy. Which is why I am asking, is bullet design and velocity more important than energy? (And honestly not trying to argue with you...lol)
Years ago there was an article in a gun rag where they shot pig carcasses and cow carcasses, they figured out how much force was need to disrupt its organs. I believe they applied that to other animals. Bullet technology has changed so much since then that minimum energy levels may have too.

For myself, I am not comfortable shooting large animals past 500 yards. That is a long ways for me and I aint got the best luck. I feel more satisfied sneaking up and getting close to my target when hunting, every guide I have had has told me stories of that "Long Range Guy".

Last edited by Radar; 01-11-2019 at 11:54 AM.
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Old 01-11-2019, 12:10 PM   #20
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Quote:
Originally Posted by Balcones_Walker View Post
As they say, there's no replacement for displacement.

What we're really talking about is producing wound channels that have the depth and shockwave needed to near-instantly kill the animal we're hunting with a minimum of wasted meat.

Energy is the most common unit for measuring this, but is not the same thing as a "unit of wound generation, depth and shockwave". The difference is most apparent when talking about bullet caliber, where for a given amount of energy and the same bullet construction, they tend to produce larger wound channels. Which is pretty intuitive - bigger bullets make bigger holes, and bigger holes are more lethal than small ones.

Often people bring up archery in these discussions, and they should not. Arrows kill by laceration, not by creating shockwave wound channels.
Actually archery is relevant to the discussion, in certian context. A 44 mag with a hardcast lead kills much more like a bow than it killls like a 3006.
I can use the same example with it and a 22/250 as i did the arrow and 9.

Most people would agree that a 44 mag with a hardcast bullet is plenty for elk and a 22/250 is light for elk, even though the 44 has less energy. But what it has is enough momentum to shoot through an elk, although the wound channel is much more similar to an arrow than a rifle
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Old 01-11-2019, 12:20 PM   #21
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Quote:
Originally Posted by Txsurveyor2014 View Post
I think we are on the same page, but I am trying to figure out where the specific number required to kill comes from. Google just comes up with opinion, not facts for me.

Example: You need 800 fpe to kill a deer. So a hunter shoots a deer at way too extended range, and it is a bang/flop drt, but then calculates the energy at impact and it was only 760 fpe. Or hunter shoots an animal at close range and the bullet disintegrates because it wasnt designed for impact at such a high velocity, and even though the energy exceeds the stated requirement, the deer runs and suffers. Both cases contradict what we go by on required energy. Which is why I am asking, is bullet design and velocity more important than energy? (And honestly not trying to argue with you...lol)
I don't know the answer, but you give two examples that could easily be real, but probably not "average". I understand what you're saying, and the numbers "they" quote are probably derived in their collective minds, and not etched in stone. Anybody that has hunted for very long, and has shot lots of game with bullets (or arrows for that matter) will know that all scenarios are not created equally. Two similar shots, same cartridge and bullet weight, might yield two different results. Ive seen this as I'm sure you have. The guys that came up with minimum ft. lb. to kill a particular animal probably did so arbitrarily because they had to draw the line somewhere.
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Old 01-11-2019, 01:18 PM   #22
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The numbers you are quoting are what they came up with for normally accepted deer/elk rounds to penetrate the vitals. Normal will be defined as a medium bore in the .243 to .30ish caliber range. A sub big bore bullet that's got tons of energy and velocity but doesn't expand will just punch a pencil hole wound and could result in a loss. Conversely, a bullet that expands perfectly but never reaches the vitals is useless. So the short answer to your question is both are important. If you can keep the velocity above 1800fps you get the added benefit of a permanent wound cavity caused by hydrostatic shock if the bullet expands.

There is a reason that the .243win, 7-08, 308, 270, 30-06, etcetera , etcetera, are so popular with deer hunters. They flat out work at the ranges that most people shoot. When you start pushing the ranges, you need to either step it up cartridge size or use a high BC bullet to help with velocity loss. My personal preference is to do both in case something goes wrong. I use a 300wsm that has more velocity and energy than a 30-30 does at the muzzle and I use a bullet proven to expand at long range.


Big bores are a different animal and rely on their large front cross section to kill and there fore need less velocity and energy to kill vs a medium bore. Granted they still need to expand some or have a very large metplat.
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Old 01-11-2019, 01:27 PM   #23
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It's just a gun writer's rule of thumb. There is nothing really scientific to back up exactly what it takes to kill a deer or whatever else. It does not take into account bullet construction and how different bullets act after hitting the animal. It doesn't take into account bullet diameter or how big of a wound channel different bullets create. All it is looking at is the mass and speed of the projectile.
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Old 01-11-2019, 01:47 PM   #24
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The military done lots of testing, so did the FBI. Pig carcasses were used years ago to examine wound channels from different bullets and velocities. I believe a lot of numbers out there now came from that testing. I think it’s just a reference point, but it’s still useable information.
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Old 01-11-2019, 01:49 PM   #25
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Old 01-11-2019, 04:03 PM   #26
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To me its more about the bullets design to function than energy. Writers just basically pulled that out their ***** as a general rule of thumb. As long as I keep my velocity above that min. and the bullet expands I've found a dead animal, the energy might of only actually been 800 or so in some long shots. That velocity is different for each bullet you should know what that is. My 150gr long range accubonds are 1300 fps but some like Barnes copper bullets maybe 1900 fps other wise you will just pencil thru. So using that reference the LRAB might be good to 1000yds and 750flbs but the Barnes might only work to 650 yds yet still show potential energy of 1000flbs. The solids and hardcast just need enough velocity to penetrate the desired amount for pass thru or in case of brain shots to the brain. Its much more about bullet design than energy in my opinion.
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