I have been away for a week visiting a little grandson and celebrating his first birthday; and as grandfathers are apt to do, I have been cogitating the dynamics of impact ballistics
Killing power Kinetic Pulse Pellet impact Wound Channels Impact Ballistics
Both Kinetic energy loss and momentum loss to a target animal, are implied in wound channels and killing power.
The relationship seems to go something like this:
The depth of the wound channel is a product of the momentum as it harnesses force (mv/t) per unit area on the head of the pellet to penetrate the tissues.
The cross-sectional area of the wound channel seems to be relative to the kinetic energy expended which causes lateral displacement of tissue at right angles to the pellets progress through the tissues.
The wound channel volume depends upon the cross-sectional area of the wound channel multiplied by its length.
Thus, when attempting to compare killing power of one pellets impact performance to that of another, there may be a case for multiplying the momentum lost in the depth of the wound with the kinetic energy lost in creating the cross-sectional area of the wound channel. the assumption being that killing power is directly related to the total volume of disrupted tissue.
I would like to give a real life example based on research I did and reported here in October 2004.
The data briefly reads like this. Three different pellets were shot over a chronograph at 6 ft from the muzzle to establish POI velocity, kinetic energy and momentum.
Freshly killed (still hot) pest birds were located at the 6 ft mark and shot through, with the pellets then immediately passing over the chronograph which was re-located behind the birds to establish exit velocity, exit kinetic energy and exit momentum.
As the same rifle was used the result reflected a true comparison of the parameters for each pellet type for that rifle in its current state of tune.
The results were:
.22 cal 15.9 gr Exact POI V 898 fps exit 648 fps; POI KE 28.465 ft-lbs, out 14.822 ft-lbs, loss 13.643 ft-lbs; momentum POI 0.0634 slug ft/s, out 0.0457 slug ft/sec; loss 0.0177 slug ft/s.
.22 cal Predator 15.9 gr ( 16.0 gr lost 0.2 gr tip in transit so given a 15.9 gr average) POI V 893 fps, exit 485 fps; POI E 28.15 ft-lbs, exit 8.3 ft-lbs, loss 19.85 ft-lbs; momentum POI 0.063 slug ft/s, out 0.034 slug ft/s, loss 0.02876 slug ft/s.
.22 18.2 gr CM POI V 837 fps, out 531 fps (edit typo); POI KE 28.30 ft-lbs, out 11.393 ft-lbs, loss 16.91 ft-lbs; momentum POI 0.0676 slug ft/sec, out 0.0429 slug ft/sec, loss 0.0247 slug ft/s.
Now for the comparison in relation to this specific case:
.22 Exact: KE delivered x momentum conserved = 13.643 x 0.0177 = 0.2415 = Kinetic Pulse reflecting possible killing power.
.22 Predator: 19.85 x 0.02876 = 0.571.
.22 Crow Magnum: 16.91 x 0.0247 = 0.4176.
In this example the comparison of Kinetic Pulse or Killing Power shows the round nosed exact to be 42 % as good as the Predator; and the Crow Magnum to be 73 % as good as the Predator.
NOTE: In case some are wondering about pellet expansion and therefore frontal area and force per unit area, these parameters are incorporated into the KE and momentum loss to the bird in the above experiment
Discussion: OK, I know dead is dead so we'll by-pass that one and we know that accurate head shots on small animals kill rather well regardless of pellet type. So our focus is in heart lung and marginal KZ strikes.
To kick it off: No, neither I, nor most probably anyone else, has down range data at hunting ranges of say 30 to 75 yards to allow examination of the effects of relative losses of velocity etc within animals of various thicknesses.
So , we might look at the picture as it may be if the pest birds had been big enough, or far enough away down range, to have stopped all three pellets in this test without pass-throughs: then: the exit velocity, KE and momentum would be zero and the KE and momentum lost to the animal would be equal to the POI figures.
So, the Exacts would have a Kinetic Pulse of 28.465 x 0.0634 = 1.8047.
The Predators would show 28.15 x 0.063 = 1.7735
The CMs would show 28.30 x 0.0676 = 1.913.
Then, although there is little difference in the figures, the order is CM, Exact, Predator at this range of 6 ft.
However, we know that the BC of Exacts is significantly higher than Predators or CMs and that .22 CMs are renowned for poor accuracy beyond 30 to 35 yards.
Therefore, I would assume that the further the range and the thicker the animal, the better would be the Exact pellets POI figures relative to the other two and therefore Kinetic Pulse would reflect that and the Exacts would ultimately rule due to better momentum and Kinetic Energy conservation. They are also more accurate at longer range and so better able to deliver to the KZs. ( My experience in shooting a fair number of rabbits at and around 150 yards with just 875 fps MV attests to that).
Summing up: Which pellet will do the most damage, at a particular range, will depend upon which delivers the best combination of momentum and KE. Dead now depends upon that combination being delivered to the vitals in proportion to the size and thickness of the animal.
I commend to you James Hall's Kinetic Pulse in the study of bullet impahttp://www.mindtinker.com/math/kp.html
and offer my interpretation based on one specific and certainly not all encompassing study example.
Kind regards, Yrrah ( I'm for bed soon so will attend discussion, if any have read this and made comment, in the morning OZ time ).