KE Transfered vs. KE Retained

[John in WI]

I'm wondering if someone could help me read a chart that I snagged a screenshot of off of Brass Fetcher on Youtube: http://www.youtube.com/watch?v=0yYYeICHamc

It's showing the "kinetic energy retained" dropping linearly with penetration depth, which makes sense if the bullet mass is not changing (ie, it's just slowing down).

But on the same plot it's showing "kinetic energy transferred" as being more or less horizontal.

But my thinking tells me, the bullet hit the gel with some KE (1/2 MV^2). The energy the bullet has drops with depth simply because it's slowing down. But doesn't energy have to be conserved? If that's the case, the energy transferred should mirror energy retained (a line with an opposite slope of the KE retained).

What's also confusing me is--how can the KE Transferred EVER go down? The plot is showing it increasing until about 1" penetration, then down, then up again at about 3". BUT--once the energy is transferred, it's transferred.

I'm just not seeing something here.

[303Guy]

The bullet yaws as it penetrates. The two energy lines are not linear but exponential, it's just that the transferred energy is much lower down on the graph but it curves down to zero at the same point the retained energy reaches zero. The 'bumps' in the curve of the transferred energy don't appear to match the retained energy exactly because E=½mv². The transferred energy line does appear to have a linear component between the two big bumps and after the second bump. The scale is too small to show the actual curve (if it exists). Interesting.

[44man]

Not in the real world when shooting animals. All energy figures on paper or penetration testing is so much junk. Energy DUMP is a myth as is muzzle energy. Energy is never lost but can be changed to heat, etc. Even your grill is hot close but changes to smoke and cools down the farther you get from flame.
The final word is always bullet/boolit work in the right place without a loss of penetration. Energy lost after penetration means nothing as long as the bullet worked. You can kill three animals in a row if all is right. You can't kill the first animal if it is wrong.
Energy is so important but it must be applied properly. !" or 3" means you shoot bean bags.
Blow a gallon jug with a .44--nice but what about if you need to go deeper in a large animal? Can you blow 3 or 4 with the bullet you chose or did it quit with the mythical DUMP? That energy is so pathetic you can't even move a human an inch. You must destroy tissue. Some little guns carried can not get through heavy winter clothes.
This is the .475 that blew 4 jugs, split 2 more and exited 17 jugs of water. A far cry from a little .380 but a 10mm with the right bullet can kill large animals. The wrong bullet will not.

[Grandpas50AE]

I agree with 44man, energy figures are esoteric mental exercise that means very little in real practice. The biggest key factors I've seen, in hunting anyway, is bullet construction and bullet placement - get those right and you have a humane kill every time.

[John in WI]

Respectfully, I realize that the "energy figures" do not really correlate to the "real world" performance of the bullet. If I can quote a cop friend of mine "bullets do what they do". All bets are off in the real world--with winter clothes, bone...

But from the figure in the video, the energy profile they are reporting is indeed correlated to the bullet. And in this (very idealized) situation, you can know exactly how fast the bullet is going (because you can see it).

And since energy is not created or destroyed--it's just changing form--my question is why are the "energy retained" and "energy transferred" curves the same shape, but mirror images? Ie, the "energy transferred"=0 until it hits the gel, then increases. The "energy retained"=100%, until it hits the gel, and then starts to drop (because it's losing speed).

I was just wondering how you are supposed to read a diagram like this.

[shooter93]

Somewhere I have an article written a few yrs ago in Precision Shooting magazine that delt with what they termed as Terminal Sectional Density, you may be able to get a copy from them. It was very well done and explained why cast bullets preform WELL above their "paper ballistics" If I find it I'll run copies but my stash of shooting/loading books and articles will soon have my house taken over.

[danski26]

I watched the video and studied the charts and I see a few problems. As you point out, energy isn't made or destroyed and its "transfer" to a different form is a linear proposition.

Now, one of the problems I see with this experiment is "transfer" is not defined. Does it mean the energy form the projectile is changed into a temporary wound channel x inches wide? Or the velocity of the gelatin moving away from the projectile as it passes? Or the amount of heat caused by the friction of the bullet moving through the gelatin? Or the light waves caused by the projectile? Or.......?

All of these factors "rob" energy from the projectile. Measuring one of them is not a complete picture of what is happening here.

All in all I would say poor experiment, poor graphs and poor conclusion.

IMHO momentum is a much better predicter of "energy" of a projectile than KE.

Also.......I LIKE IT WHEN I CAN COMPLETLY AGREE WITH YOU 44MAN! ;-)

[williamwaco]

Some of the energy is "transferred" into bullet deformation.

That said. The chart doesn't make any sense. At the right side of the chart, the energy transferred should equal the total energy on entry unless the bullet exited the block.

Energy retained + energy transferred MUST equal the initial energy.

I wonder if the energy transferred figure is not mislabeled or miscalculated.

I did not watch the video.

.

[44man]

Some of the energy is "transferred" into bullet deformation.

That said. The chart doesn't make any sense. At the right side of the chart, the energy transferred should equal the total energy on entry unless the bullet exited the block.

Energy retained + energy transferred MUST equal the initial energy.

I wonder if the energy transferred figure is not mislabeled or miscalculated.

I did not watch the video.

.
I agree. Yes, you might even get LIGHT! I don't see any way to measure energy change but energy transferred will equal what it started at. Even the weight of gelatin blocks from shot to shot will change it.
Tissue hit in an animal will change transfer. So will the size of the animal. Very large beasts seem to not even notice being hit.
Even deer hit hard can jump and then just stand there or walk off a ways.
Energy is never destroyed. A light bulb changes energy to light and heat but in the end, it is equal to the energy applied.

[John in WI]

"Energy retained + energy transferred MUST equal the initial energy."

that's exactly it William--conservation of energy!

There is something funny about the way they have this plotted. I would believe the "KE Retained" plot--it makes sense that it's dropping as the boolit is slowing down. (from about 800 to about 100FPS). The KE Transfered plot makes absolutely no sense to me!

[NSP64]

Hi,
Energy is measured in fps.
transfer of energy is also measured in distance over time.
the energy is transferred in amounts all along the bullets path.
if it stopped in the first inch you would see a complete "dump " along the length and time of the bullet moving through the object.
changes in shape will effect the deacceleration rate/distance.
The sum total of energy transferred over the length of the path should equal the amount the bullet had when it first entered.
unless you can measure velocity at points along the route, its all guess work.

It is a fun thing to play with , but has no real meaning in real world situations.