theoretical question about wound ballistics

[Luger]

As far as I understand this topic, a bullet fired from a handgun (regardless of design) is usually only able to damage tissue by directly hitting and crushing it. Temporary cavitation is usually irrelevant to the wound profile. With a bullet fired from a high powered rifle on the other hand, the much larger temporary cavitation may in fact damage tissue by stretching and ruptering it. (I`m aware of the fact, that this effect depends on jawing, fragmentation or deformation of the bullet.)

The reason for this becomes obvious, if I compare a 124gr 9mm bullet traveling at about 330m/s and with about 450 Joule of energy to a 62gr 5,56mm bullet traveling at about 920m/s and with about 1.700 Joule of energy. The rifle has nearly 3 times the velocity and nearly 4 times the energy of the handgun.

So far so good. But where is the point, at which a bullet gets the potential to be so much more devastating? Is it a matter of energy (for example more than 1.000 Joule)? Is it a matter of velocity (for example more than 700m/s)? Or is there another mechanism, of which I`m unaware?

[scw2]

I believe the guys In the lucky gunner video on ballistics (posted in other thread) mentioned 2200fps

[Tabasco]

Here's the link to the LG article/video mentioned:

https://www.luckygunner.com/lounge/w...ics-gel-works/

[Luger]

Well... A 4,6mm bullet fired from the H&K MP 7 travels at about 2.370 fps. This would mean, it passes the 2.200 fps line.

But as far as I understand Doc GKRs articel on this topic, it is not more (maybe even less) effective than common handgun rounds.

So either the bullet has to go much faster, or the effect depends on another mechanism than velocity?

[BehindBlueI's]

I don't know the "when" but per my reading it occurs once the projectile causes tissue to expand faster than it can do so without rupturing/tearing. Each type of tissue has a certain level of elasticity and as long as you don't exceed that level it will go back into place without injury. So it can't *just* be velocity or *just* energy, it's how the projectile interacts with the tissue and disrupts it.


There's a direct analogy in demolitions. Energy alone doesn't tell you how much damage you are going to do with a given charge. Speed of the shock wave, the shape of the charge, etc. matter a whole lot.

[the Schwartz]

As far as I understand this topic, a bullet fired from a handgun (regardless of design) is usually only able to damage tissue by directly hitting and crushing it. Temporary cavitation is usually irrelevant to the wound profile. With a bullet fired from a high powered rifle on the other hand, the much larger temporary cavitation may in fact damage tissue by stretching and ruptering it. (I`m aware of the fact, that this effect depends on jawing, fragmentation or deformation of the bullet.)

The reason for this becomes obvious, if I compare a 124gr 9mm bullet traveling at about 330m/s and with about 450 Joule of energy to a 62gr 5,56mm bullet traveling at about 920m/s and with about 1.700 Joule of energy. The rifle has nearly 3 times the velocity and nearly 4 times the energy of the handgun.

So far so good. But where is the point, at which a bullet gets the potential to be so much more devastating? Is it a matter of energy (for example more than 1.000 Joule)? Is it a matter of velocity (for example more than 700m/s)? Or is there another mechanism, of which I`m unaware?

Trying to set a 'hard' limit at which distant velocity-related effects start to occur based on velocity alone is never a good approach as it considers only part of the picture. Damage done to tissue by a bullet is also a function of the type of tissue being struck. The velocity at which that particular threshold is reached varies with the type of tissue being struck.

Tissues with greater elastic and compressive yield strengths (like lungs, much of the GI tract, for example) will require much higher velocities before distant effects start to occur. More fragile tissues (like the brain, liver, spleen, kidneys, pancreas, etc.) will see distant effects begin to occur at much lower speeds.

Bullet shape, drag coefficient and cross-sectional presentation/expansion area also play significant roles in determining at what speed such effects start to occur.

[DocGKR]

Which is more destructive:

[Luger]

The most destructive bullet seems to be the one with the best balance between velocity, weight and fragmentation.

If I get this right: A light and fast bullet can fragment and cause a impressive temporary cavitation. But if the bullet gets too light, penetration will be too shallow and all the velocity will be useless. This get`s even worse, if you drop down to the energy level of a handgun or SMG/PDW.

A slow and heavy bullet on the other hand will not fragment, but penetrate reliable and (if it deforms or jaws) cause a big temporary cavitation. (Wether this is big enough to damage tissue depends on bullet placement.) So it will be less effective than a bullet with optimal balance, but clearly better than a verry light and fast bullet.

Is this correct?

[Tabasco]

The most destructive bullet seems to be the one with the best balance between velocity, weight and fragmentation.

If I get this right: A light and fast bullet can fragment and cause a impressive temporary cavitation. But if the bullet gets too light, penetration will be too shallow and all the velocity will be useless. This get`s even worse, if you drop down to the energy level of a handgun or SMG/PDW.

A slow and heavy bullet on the other hand will not fragment, but penetrate reliable and (if it deforms or jaws) cause a big temporary cavitation. (Wether this is big enough to damage tissue depends on bullet placement.) So it will be less effective than a bullet with optimal balance, but clearly better than a verry light and fast bullet.

Is this correct?

Not answering for Doc, but I am familiar with the above illustration.

The 'balloon' you see along the bullet's path is the temporary cavity. Within that temporary cavity, there is a darker area which is actual damaged tissue. The green line is the minimum required penetration for good performance. The 40gr. .556 damages tissue within the temporary cavity due to high velocity and fragmentation (good), but does not meet minimum penetration (bad). The .45-70 over-penetrates (bad), and only damages tissue along its path by crushing the tissue it encounters (not so good). You get a probably .50 or .60 caliber wound, as the velocity is not sufficient to cause damage within the temporary cavity. The ideal solution is the middle illustration, where you have velocity greater than 2000 fps., which creates damage within the temporary cavity (good), and penetration beyond the minimum required without over-penetrating (good). Hope that makes sense.

[DocGKR]

BehindBlueI's and the Schwartz pretty much hit it out of the park.

Substantial temp cavity effects can be seen with a shotgun slug at 1500 fps, while minimal tissue damage can occur with a .224" rifle projectile at 7000 fps--all depending on bullet upset. Likewise, as noted, the type of tissue subjected to stretch is also a critical component in assessing injury potential.