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>> Power Factor On Bullet Impact :: By James C. Gates on 2001-09-12
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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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