Energy calculation...

the equation for energy is e=.5*m*v^2 But you have to get mass in the correct units which is Slugs. To do this divide the mass of the bullet in grains by 7000 to get it to lbs, then by 32.17 to get it to slugs. if you combine those and the .5 you get 450380. so the equation woudl now be e=m/(450380)*v^2

I've always done it with grains. Velocity X velocity X WT in grains divided by 450240 = Ft Lbs energy.

Or so I've always thought.

ttbadboy, I think the answer to your question is more complicated than you are thinking. Energy delivered to the target is the desired outcome. Because of temporary and permanent wound cavities the simple answer is confounded by bullet design and what it has to penetrate before entering the target (denim, t-shirt, buffalo hide, ...).

On this site we still have raging arguments as to whether it is better to cause leaking holes or an expanded slug that remains in the target.

Hmm, kinetic energy is 1/2 mass * (velocity squared), as given above. Momentum is m * v. So they describe the same thing. You can't get more or less of one without the other. As it happens, kinetic energy is a "scalar" value while momentum is a "vector" (requires a direction to be complete). But that doesn't matter here since we know what direction the bullet is travelling.

Do you mean is it better to have mass or better to have velocity? If so, I'll let others answer since it gets into the quagmire I mentioned before. Because of air resistance, bullet trajectory and energy at long range has to factor in "sectional density" but that doesn't mean much at 7 yards.

"To rephrase the question a little: what makes for more damage potential, ignoring all other factors: more momentum with less energy, or more energy with less momentum?"

Since I have never taken part in one of the quagmire discussions...

It seems clear to me that energy is most important (for hunting or defense) because once the bullet strikes the target, it will need to do work on it. F dot d.

Tim

momentum vs Kenitic Energy

This is the underlying question that has been debated since late in the 1800's. It is usually asked "which is better a big heavy slug going slow (momentum camp) or a smaller bullet going faster (KE camp)?

For a given weight bullet as the velocity goes up both momentum and KE will go up, just KE goes up much faster. Thus the argument for high velocity small bullets. Taken to extreme, compare getting hit by a grain of sand at mach 10 versus getting hit by a supertanker at 10 knots. The sand may well bore a hole right through you but the tanker will tend to squish you against the pier.

Personally I think you need both. I have heard of high KE bullets being used in Africa against Zebra with disasterous results. They tend to blow out chunks of skin and leave a shallow crater and a really pissed off zebra. Weatherby's in particular have developed a bad reputation because of this. Often this is compounded by errors in bullet selection. A bullet that will hold together at normal velocity won't necessarially hold up at magnum velocity. So pick a tough bullet that is heavy for caliber.

I wrote a program to calculate energy using Visual Basic...

This program only works with ".net" compatable computers however...

If you try it and it doesn't work, go here:

Microsoft.com

And download that update... then it should work...

As far as damage incurred, momentum is more important. You have to have the mass to do the damage. Beyond a certain point, all velocity does is localize the damage.

Imagine a car hitting a medium-sized tree at 5mph. It might kill the tree by breaking the trunk somewhere along the length or by lifting the roots out of the ground. Basically, the tree will break at it's weakest point. Now imagine a motorcycle hitting the same tree at 20 mph. It'll damage the tree at the point of impact, but the tree will live to photosynthesize another day. Finally, imagine the car hitting the tree at 20mph. It will kill the tree and the damage will be at the point of impact instead of wherever the tree felt like breaking.

The more mass you have, the less velocity you need to do the same amount of damage (Imagine a tractor-trailer doing 1mph against the tree), but if you want to localize the damage and impart penetration, you need a certain amount of velocity too. Frontal surface area plays it's part too. A flat surface allow the force to be distributed better than a sharply pointed object.

So, light fast and pointy should make a good pentrator, but no do a lot of damage. Hmmm, sounds like the SS109 to me. And heavy, slow and flat should impart a good deal of force, but not penetrate. Sounds like the classic .44 special steel loads.

Mikul, what about the temporary wound cavity? If it stretches large enough the projectile does much more damage than its mass value? And isn't that mostly a factor of velocity?

Energy delivered to the target is the desired outcome.

Click to expand...

Ummm no. The desired outcome is that you kill the guy or at least get him to stop shooting at you. You cannot make the claim that kinetic energy (or momentum) is a direct measure of the likelihood of either of those two things. The best you can say is "as the trend..."

Hmm, kinetic energy is 1/2 mass * (velocity squared), as given above. Momentum is m * v. So they describe the same thing. You can't get more or less of one without the other. As it happens, kinetic energy is a "scalar" value while momentum is a "vector" (requires a direction to be complete). But that doesn't matter here since we know what direction the bullet is travelling.

Click to expand...

No again. Kinetic energy and momentum have a derivative relationship. They are not the same thing anymore than acceleration and velocity are the same thing. Plus kinetic energy is a scalar and momentum is a vector which is important because it changes the whole nature of conservation of these values. Energy must be conserved but kinetic energy does not. Momentum must always be conserved.

In general momentum is a good damage indicator for soft targets like people. Kinetic energy is a good damage indicator for hard targets like body armor. Momentum is a fair measure of how much someone will feel a bullet impact subjectively because that person must feel the impact effect that much (conservation).