How do you accurately measure the temporary and permanent wound channels in soft tissue?[/QUOTE said:
The short answer is "you can't".
Soft tissue covers quite a bit of ground. Skin, fat, fascia, tendon, muscle, lung, nerves, vessels, brain, liver, spleen, myocardium, and bowel are all soft tissues but they have petty different properties in tensile strength, density, and how they react to penetrating trauma. Consider entry and exit wounds in skin. Even when they result from a GSW of the same caliber, they can vary in size and configuration greatly from slit like, to considerably larger than the projectile diameter. Tissues like liver, spleen, and brain parenchyma have little to no connective tissue maintaining integrity. They are basically held together by dura or capsules to a considerable degree. GSWs in these tissues can cause extensive irregular tissue fragmentation.
Considering only muscle parenchyma (not including the investing fascia), since this is what many think off when they hear "soft tissue" and is what 10% calibrated ballistic gelatin is said to simulate, you cannot measure temporary cavity by any means. The tissue is elastic (unlike gelatin) and may undergo significant displacement with passage of a projectile, but then will recoil back into place. Some high velocity rifle projectiles can cause devitalization of some of the muscle tissue that undergoes rapid stretch, but this often does not happen, and when it does it is irregular and sometimes not apparent at the time of initial wound exploration. At any rate, there is no way to measure this type of effect with any precision.
Projectiles do create permanent crush channels through muscle tissue, but these are not like precise cylindrical channels bored through metal plate with a carbide bit. The channels are irregular and may be distorted by hematomas. You can't apply a caliper and measure their diameter.
What a surgeon can do at the time of exploration is determine when a projectile has hit, or very barely missed a critical structure. There will be times, albeit fairly rare, when a projectile has barely missed such a structure where one of slightly greater diameter would have resulted in a dramatically different outcome.