Perhaps I did not state the concepts clearly which I was trying to convey (unless your question is rhetorical). Rifle rounds have much higher KE and much higher Velocity. It's that combination that causes a massive hydrostatic pressure wave because the soft tissue can only be moved out of the way so far and stretched so far before tearing, being mostly water.
That pressure wave causes additional tearing (especially with bullet fragments that have already weakened tissue radially around the point of fragmentation), making a vastly disproportionate wound relative to the projectile size. It's that resistance to the projectile that obviously also causes the bullet to fragment, having pressure around it's frontal area, especially when they yah and have a cannelure which weakens the frontal region. When turning sideways to any degree, we now have even MORE area with pressure on it and it breaks apart.
This is one reason why fleet AOA issues caused inconsistencies in M855's fragmentation ability even at very close ranges (0 to 50 yards) with through and through hits. Because it is also velocity dependent, at intermediate distances it once again becomes a problem because now regardless of AOA, the hydraulic pressure against the projectile is no longer high enough to cause fragmentation (typically 150 yards for a M4 and about 200 yards for an M16).
That's the very reason many hand gun rounds actually penetrate deeper, because they have high momentum (heavy) and low velocity. So they do NOT create that large pressure wave (rapid transfer of energy), do not fragment and only provide in some cases mild expansion to slightly enlarge the permanent wound cavity. It is that conservation of energy that allows them to stay in motion until all of it has been transferred from the projectile to the target. The slower that process, the further it will penetrate. Rifle rounds would typically penetrate even deeper if they do not expand or fragment, but even many SBR's achieve that at closer ranges. Combine the reduced KE, momentum with still reasonable expansion and penetration suffers (unless that load is over driven in a longer barrel).
It is for that very reason you can "over drive" certain hollow points that have ideal penetration to expansion ratios but when hot loaded (+P+) to the limit, may suddenly have inadequate penetration. They expand more rapidly and to a greater degree at higher velocities, thus transferring their KE more rapidly. The problem is with handgun rounds, the additional expansion isn't really enough to overcome the tissues elasticity, but the drag is higher, so they tend to NOT create a larger wound while simultaneously suffering inadequate penetration. Kind of a sucky situation. Federal HST and Speer Gold Dot's are two of the most consistent loads for expansion, but some of the super hot +P loads over drive them and result in barely adequate penetration.
Aside from that specific instance however where you primarily changing bullet weights, taking a heavy vs a light load, the heavy load typically will penetrate deeper even if it achieves nearly identical expansion due to it's higher momentum (again, pending over expansion does NOT counteract that by increasing it's drag in target).
Momentum is thus a better predictor of penetration on average than KE pending the projectile design does not change considerably. We all know that 110gr projectiles tend to penetrate deeper than 85gr projectiles even if both are hollow points of the same over all constructions and the KE at the muzzle is the same. The combination of lower velocity (less expansion) and higher momentum both play a role, but momentum seems to more reliably predict penetration depth.
I was not in ANY way trying to argue that handgun rounds out perform rifle rounds in wounding (volume of tissue actually damaged). However compared to SBR's, many common hand gun rounds actually penetrate deeper, but have a very small permanent wound cavity, thus making them less effective. That is due to their high momentum to low expansion properties.
I am not arguing with these studies on wounding: see attachments. I'm simply suggesting momentum is more useful for determining weather a load is likely to have adequate penetration than just it's KE which people often see as a necessity for deep penetration with heavy loads.
Terminal ballistics are dynamic and can be very baffling. There are a lot of factors at work and there is no simple formula that will come close to explaining it. I'm sure someone could come up with a formula, but it would be very long with a lot of variables. Momentum and kinetic energy are used because the weight and speed of a bullet are major factors, but also because they're very simple to work with.
I mean no disrespect, I am trying to clarify things a bit, some of your explanations are comparing half of an apple to half of an orange and then adding some bananas and grapes making for a fruit salad explanation.
Momentum= MV
Kinetic Energy= 1/2MV²
Pressure is force applied over an area. P=F/A
Hydro neans fluid. Static means still. Dynamic means changing.
Our old buddy Sir Ike Newton's, explanation in regards to Conservation of Eomentum and Energy: An object in motion tends to stay in motion until acted upon by another Force. He also states, For every action there is an equal and opposite reaction.
In both formula, Momentum and Kinetic Energy, speed the multiplier. Speed is more important in kinetic energy because velocity is squared and the mass is halved. Momentum is what keeps the bullet moving. Kinetic energy is the stored energy of the moving bullet and a good indicator of what the bullet is capable of doing when it strikes a target.
Handgun bullets do not penetrate deeper simplely because they are moving slower. They penetrate deeper because they have not used a lot of energy on expansion or fragmentation, because they simply do not possess the energy, and have the structural Integrity, to expand
and penetrate. The +P+ handgun bullets will expand or fragment violently with very little penetration, because they now have enough speed to contribute to the energy and overcome the strength of their construction. Fast moving rifle bullets that have lower momentum, but don't spend energy on expansion or fragmentation, will penetrate extremely deeply.
A tumbling bullet may fragment because force is applied to places it was not designed to withstand. When a bullet turns sideways to its path of travel pressure is not increased, it is decreased because you now have a larger surface area. A bullet traveling sideways, or tumbling, creates a larger wound channel simply because it is more surface area being forced through tissue.
Fired from a SBR:
55 gr 5.56mm @ 2300 ft/s
Area: 0.039in²
Momentum: 56 slug ft/sec
Kinetic energy: 646 ft·lb
147gr 9mm @ 1200 ft/s
Area:0.099in²
Momentum: 78 slug ft/s
Kinetic energy: 470
The 9mm has a 60% greater area but only 25% more Momentum. The 5.56mm has 27% more energy and about double the pressure. The instant the bullets strike the target all of these calculations change. Depending on how the bullet is constructed (what it is made of as well as its shape) and what the target is made of will determine what happens next. These forces will be easy to calculate
only if the bullets were and stayed cylinder shaped like a wadcutter. Throw in a round or very aerodynamic tip and calculations get much more difficult. Add bullet expansion, fragmentation and a tumble and you'll wear your calculator out. Xfrog has witnessed and explain the difference in wound channels between an aerodynamic bullet and a wadcutter.
Centrifugal Force= MV²/r
Another important and often overlooked force is the energy in centrifical force of the spinning bullet. Centrifugal force is a form of kinetic energy. Rifle bullets spin faster, not just because they need more twist to stabilize their longer length, but because they're traveling faster. Centrifical Force assist in bullet expansion and fragmentation. It can be a major factor in temporary and permanent wound channels. X-Man has documented some of the effects centrifugal force has on wound channels. I believe centrifugal force contributes to, "...a vastly disproportionate wound relative to the projectile size". A larger bullet will have a larger wound channel than a smaller diameter bullet. An expanded bullet will have a larger wound channel than a non-expanded bullet. An expanded bullet that fragmentation, will have an even larger wound channel.
All of these formulas are taken in a static moment of time. Terminal ballistics are very dynamic, they can be calculated moment by moment with these formula, but with every consecutive moment, a new set of calculations is needed.
