Energy vs Velocity

[Txsurveyor2014]

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?

[diamond10x]

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.

[Jared.King]

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.

[Txsurveyor2014]

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.

[Drycreek3189]

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.

[RJH1]

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

[Txsurveyor2014]

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.

[StrayDog]

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.

[BrianL]

E=mv ²

It all works together.

[Radar]

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.

[Jared.King]

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.

[RJH1]

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

[Txsurveyor2014]

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)

[Radar]

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.

[BrianL]

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.