In trying to determine a good load to a 6mm cartidge I am developing handloads for I came to an old question that I still don’t have a firm understanding of.
In this particular instance I have two 6mm loadings. One is a 75 grain Flat based spitzer at 3000 FPS. The other is a 95 grain boat tail match bullet at 2500 FPS(I may be able to wring a bit more velocity out of this load).
The 75 grain load, not suprisingly delivers quite a bit more energy than the 95 until 600 yards or so.
A similar comparison would be the 5.56 M-193 vs the MK262. The M-193 has more energy from the muzzle but the MK 262 with it’s 77 grain bullet is thought to be the more effective round.
How do we reconcile a bullets energy with it’s actual effectiveness?
Energy doesn’t do any good if it doesn’t dump into the target. The mk262 is a better round for a lot of reasons but consistent performance is a main part.
I don’t think it is possible to make a correlation directly between energy and performance.
We don’t–at least, not legitimately.
Energy, in and of itself, has no wounding capacity (we are limiting to physical trauma.)
Additionally, the kinetic energy of a bullet is a very poor proxy for predicting terminal performance.
For example, consider four injuries to the quadricep muscles:
a hard punch from an athletic woman.
a .22 short gunshot with no exit wound.
a 500 grain broadhead hunting arrow at 200 fps that stays in the leg.
a deep laceration from a razor-sharp butcher knife.
The punch delivers the most KE but does the least damage; while the butcher knife does the most damage with the least KE, and the .22 short has about 50% more KE than the broadhead arrow but does much less damage.
While a bullet must have some KE–a bullet with no velocity does no damage–KE is a very poor predictor of a bullet’s performance.
I would say that there are certain desireable velocities (and thus by extension kinetic energies) for a given bullet in order for its design to work as intended, but beyond assisting the bullet in fragmenting or opening up the energy does nothing but physically get the bullet from the chamber to your target.
Physics. Its real. Kinetic energy is simply a measure of the work potential of a projectile. As noted above, although part of the equation, kinetic energy in and of itself it is not a predictor of incapacitation effectiveness. Recall:
– Bullets cannot physically knock down a person by the force of their impact.
– Kinetic energy or momentum transfer from a projectile to tissue is not a wounding mechanism.
– The amount of “energy” deposited or momentum transferred to a body by a projectile is not directly proportional to the amount of tissue damage and is not a measure of wounding power.
– Wounds of vastly differing severity can be inflicted by bullets with identical kinetic energy and momentum.
What a bullet does inside the body–whether it yaws, deforms, or fragments, how deeply it penetrates, and what tissue it passes through is what determines wound severity, not KE!
Kinetic energy can tell us how much a projectile might overcome tissue-wise, if we know surface area of the projectile and the resistance value of the tissue being addressed (Figuring it takes a certain amount of energy to traverse 1 cm of tissue), so it gives us some idea of penetration factors.
However, you are absolutely correct, when looking at wounding characteristics, kinetic energy doesn’t tell us much of anything comparative to actual destruction of tissue.
If you want a thorough understanding of the phenomena, I would recommend highly that you get and read, “Bullet Penetration: Modeling the Dynamics and the Incapacitation Resultng from Wound Trauma” by Duncan MacPherson. It’ll answer all of the questions that you might ever have.
In his book, MacPherson provides equations that permit the calculation of terminal penetration and permanent wound cavity mass so long as you can provide retained mass, impact velocity and an average recovered diameter.
The calculations are a bit onerous to punch into a calculator repeatedly so my extremely lazy nature compelled me to put them into an Excel speadsheet in order to save myself from all of that unnecessary labor.
