Some Thoughts on Energy Transfer
We know that as a projectile moves
through the air it has Kinetic Energy based on
velocity and weight. We also know the
that velocity attained at the muzzle was
created by pressure (in pounds per
square inch) applied to the area of the base of the bullet. Otherwords,
Kinetic Energy was stored in the bullet by acceleration for zero velocity to
muzzle velocity. Energy was transferred from the pressure of the burning powder (pounds
per square inch) to the mass of the bullet (foot pounds of energy).
This is rather straight forth Physics. We also know that stored Energy, that was
attained by acceleration, is in turn lost by deceleration. As the Energy is lost
in an object, the process is called Energy Deposit, or Energy Transfer.
Now, how this Energy Deposit is applied to the Killing Power on game is a very
controversial subject, to say the least. Many experienced hunters have struggled
for years to establish a formula to explain the process. No one has come up with
an ironclad method and I don’t propose to either. I do plan to suggest some
possibilities that apply to this Energy Transfer. I am not going to bore you by
restated all the various formula, such as Momentum, Taylor’s Knockout, and all
the others. It is not my purpose to try to incorporate them into my
presentation.
Experienced researchers have proven
that by changing the frontal area of a projectile, the apparent cavity in test
gel and living tissue is larger, or smaller, as the case my be. They have also
proven that by maintaining the frontal area and increasing the velocity, the
cavity increased. This is logical since the increase in velocity adds Kinetic
Energy stored by the bullet. This increased Kinetic Energy is then transferred
to the object or living tissue.
Now we come to the argumentative part
as to how this Kinetic Energy is transferred and just what it does!
First off, let’s think about what we
know about ballistic gel and living tissue. We know it comprises of
mainly water and water can not be compressed! Therefore, under pressure
it becomes a solid. Apply heat and it becomes a gas in the form of steam. I
do not believe a bullets impact causes enough heat to convert the water in
tissue to steam. The blood mist we see at times, when a bullet penetrates living
tissue, is just that...a mist. In extremely cold weather, where the
animal’s internal temperature is much higher than the outside temperature, it
may taker on the appearance of vapor (much like the vapor from your breath). So
much for steam. With this in mind, is it not possible that the water, in a
compressed solid state being forced aside by the meplat of the bullet, causes
the destruction of tissue?
If you accept that possibility, we go
on the study what might be happening. We accepted earlier that pressure applied
to the base of the bullet, during acceleration stored Kinetic Energy (foot
pounds per square inch) , based on muzzle velocity.....then is it not possible
to apply the same principle to the area of the bullets meplat, as it decelerates
in living tissue?
I think this Kinetic Energy is
transferred from the Meplat to living tissue as the bullet decelerates due to
resistance. In a hard cast bullet, the meplat remains the same area in square
inches. The bullet that is designed to expand on impact, has a constant
expanding meplat and a much quicker deceleration, thus causing a larger and
shorter cavity. This can be seen when examining wound channels between hard cast
bullets and expanding. Since expanding bullets are not the prime interest of our
cast bullet shooters, lets move on.
Although, I do not think a formula can
the established, I do think we can set up a method of relating the possible
tissue destruction between various bullets. In physics, we know that for an
Action there in an equal reaction. Also we know that Force (KE) is directed
along the axis of the projectile. Therefore, if KE was stored by pressure
applied to the area of the base of the bullet, it in turn will be transferred
(released) by the frontal area of the meplat. By dividing the area of the meplat
of the bullet by the area of the cross section of the bullet, a percentile of
the Impact Energy is arrived at. This is the amount of KE stored on the meplat
vs. KE that is stored on the area of cross section of the bullet (area of base).
Therefore, the higher this percentile is(the more KE is transferred) the larger
the permanent wound channel will be (as long as weight and velocity remain the
same).
Now, let’s look at some examples
to see if this is logical:
Area of cross section Area of Meplat
% Velocity Energy % Transferred
( Note on Velocities...These are
chroographed figures by shooters/handloaders)
(1) Beartooth LBT .432” 265 gr.
Bullet..................................................................
.432” @ .1465 sq in .340” @ .0907
sq in .6191 1260 fps 934 fp 579 fp
(2) Beartooth LBT .432” 265 gr.
Bullet
.432” @ .1465 sq in .340“ @ .0907
sq in .6191 1400 fps 1154 fp 714 fp
(3) Beartooth LBT .432” 265 gr.
Bullet..................................................................
.432” @ .1465 sq in .340” @ .0907
sq in .6191 1565 fps 1442 fp 893 fp
(4) Beartooth LBT .358” 185 gr.
Bullet..................................................................
.358” @ .1006 sq in .280“ @ .0615
sq in .6113 1400 fps 805 fp 492 fp
(5) Beartooth LBT .358” 185 gr.
Bullet..................................................................
.358” @ .1006 sq in .280” @ .0615
sq in .6113 1730 fps 1230 fp 752 fp
When these “% Transferred” figures
are compared with actual experience....they seem to fall in line with what we
have seem on the destruction of living tissue. Do the figures really show how? I
am not ready to say yet!
So.......Where are we? We have not
developed a formula to calculate killing power, but have set up a Factor method
to compare the potential energy transfer of various bullet/loads in hard cast
alloy bullets...........Your comments are welcome, but do your research first!
James C. Gates@bellsouth .net (Revised 9/11/2001)
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