The reason accuracy degrades in most bullets as they pass through transonic is that in general, most bullets are overspinning at that point in their flight. If the axial drag and the horizontal drag of a bullet is balanced from the muzzle then this overspinning (sometimes erroneously called overstabilized) does not occur. When a bullet is spinning faster than necessary to keep it pointed nose forward it starts to precess and yaw. The nose is a little high and to the right(for right hand twists) and is drawing little circles in the air. The greater the spin over what is necessary the greater the precession and yaw. Most bullets have axial drag numbers that are much less than their horizontal drag and, therefore, the spin rate relative to what is necessary is always increasing. This means that when they get some 1000+ yds. downrange and are approaching transonic their precession and yaw is much pronounced. During transonic passage the shock waves are collapsing directly around the bullet. When a bullet is overspinning, has pronounced precession and yaw, and enters transonic the collapsing shock waves exacerbates the condition leading to much greater inaccuracies and even total destabilization. If a bullet's flight, and drag numbers are balanced, the Balanced Flight Theory, it will be pointing directly into the oncoming air and can passage the transonic region quite accurately.
On a slightly different subject, energy is not a good quantifier of lethality. Any comparison of energy completely ignores the expansion and penetration characteristics of the bullet. It is the hole that the bullet leaves that causes death. The width, depth, and speed of penetration are the characteristics to measure to determine lethality. There are threshold velocities at which point a particular bullet begins to expand and penetrate differently than it would at higher velocities. These need to be known. For all intents and purposes bullet impacts at velocities below 1500 fps. need to be considered as one to one and a half caliber hole punchers as there is little or no wave effect coming from the penetrating bullet that will damage tissue. At this point energy is meaningless. Momentum and diameter of the bullet are the determiners, and of course, the all important, shot placement.
Energy, or more properly kinetic energy, is 1/2 mass times velocity squared. Momentum is mass times velocity. As you can see velocity is much less important in momentum and the importance of mass, or weight, is much greater. From this and the above discussion it is easy to see that on long shots where the bullet may be impacting at less than 1500 fps. a heavier bullet will have a greater lethality potential at that point than a lighter bullet traveling faster.
Like I said, "as it's dropping through the sound barrier, it becomes somewhat unstable and therefore less predictable"; glad to see we both said exactly the same thing.
However I would offer a different viewpoint about energy; I would maintain that energy is not "meaningless". Any bullet which does not exit an animal has in-fact transferred all its' energy to the animal. At long ranges probably the only known variable is energy. The amount of expansion of the bullet has as much to do with the design and construction of the bullet as does the amount of energy acting on it. One would obviously choose one's bullet based on the particular job one was trying to accomplish; much like one chooses a caliber based upon the job one is trying to do. So in trying to select the appropriate bullet, one needs to know the energy at a given range - from this one can select bullet type and decide if this combination is sufficient to accomplish that which one are trying to achieve. Even at quite low velocities one can achieve complete energy transfer by using frangible ammo.
Transitioning through transonic inaccurately is not a given. Folks have been doing this accurately for about 140 years. Sharps rifles shooting 45-90 and 45-120 start supersonic but go subsonic rather soon and do not have time to overspin. If you assume it cannot be done at close or long range or ever ultra-long range then you are ignoring the facts and physics.
Energy is not a good measurement of lethality. On impacts of less than 1500 fps momentum would be better, but only with bullets of the same diameter. The concept that the energy has to be transferred to the animal is not good science. I can make bullets, even in large calibers, that will transfer 100% of their energy in a very few inches. They will not be lethal in most cases.
I'd have to disagree there. The amount of energy the bullet uses up in penetration matters not. What kills the animal?
Either a CNS hit or the interuption of O2 to the brain. Substantial disruption of the blood flow to the brain is caused by the bullet tearing through blood filled organs and or arteries.
Take a barnes X, lets say that it expands the same every time. You shoot an animal in the lungs broadside, first with MV high enough to have full penetration the second with just enough to lodge just under the hide on the far side. Which did the job better? The end result is an animal that has big hole through both lungs. Whether the bullet stayed in or not doesn't effect the killing capabilities of a bullet.
Just my opinion!
[ 07-23-2001: Message edited by: txhunter ]
Warren. Your just a little to quick on the draw for me. Somebody always gets there before me.
The correlation between energy and lethality can be made using the following logic:
As bullet impact velocities begin to climb above 3000 fps. the diameter of the secondary wound channel, or that tissue outside the bullet hole itself damaged by the wave effect, begins to grow at a geometric rate. The secondary wound channel on impacts of 3500 fps. is dramatically greater than that at 3000 fps., and so on. Assuming that the bullet holds together, which at these impact velocities it usually won't, the lethality of this secondary is dramatic. Observations over the years have been made to the effect that this incremental increase in velocity was responsible for greater than expected lethality ergo the use of the energy equation which gives velocity a squared value in the equation. It is not the energy or the release of energy that kills. It is the wave effect that is much more pronounced when velocities of penetration are greater than 3000 fps.
This will always be a controversial subject but the energy requirements
that you read about are supposed to be a guideline "NOT A MUST" based
on quick one shot kills in the heart/lung area(Where most shots are made)
A case in point, Just the other day in the newspaper there was a horse
and her 7 day old fold that had been shot with a pellet rifle by some vandals.
The fold died a slow and painfull death because the pellet had gone through
Assuming you make a perfict shot every time you will not need these energy's
But this is not a perfict world and some times if the animal runs off he/she
may not be recoverd.
I like to try and use these energys when possible but sometimes have to take
a head or neck shot if I feel like I dont have enough gun for the animal or the
Shot placement and bullet choice are the most important but enough energy
can mean the difference in recovery of the animal or not.