I still think there's a concern about what happens when projectiles pass through the body at speeds greater than the speed of sound inside the body. Conventional bullets don't do that, and I wouldn't be surprised if this results in greater shock damage to internal organs than a conventional bullet could achieve.
Korto wrote:In a story, the main guy said that a Heavy Needler could fire a needle (10g 5000m/s 4mm thick 1000mm long) through "one end of the mansion to the other", through multiple heavy masonry (brick) walls. Would he have been correct, or would the needle likely have exploded hitting the first wall? (It's all right for him to be wrong, he's a merchant/pilot/starship captain, not trained military.)
If the needle material is dense and hard enough it would crash through masonry walls rather effectively, though it might not crash through all the walls in the mansion depending on exactly how many there were and how thick they were.
If the needle is made out of ordinary materials it would be likely to crater against the first thing it hits, the way that orbital debris tends to crater and spall when it strikes orbiting satellites.
I think that people are seriously underestimating the effects of a high velocity projectile on human tissue. 3 mm is about .12 inches, and 1000 m/s is about 3280 ft/s. We don't have any current weapons that exactly match those figures, BUT we do have some .17 caliber rounds that exceed that speed, such as the .17 Remington, which develops about 3800 ft/s with a 30 grain bullet. I'm having a little trouble finding ballistic gel tests of .17 caliber FMJ bullets right now, but tests of .22 caliber rifle bullets (5.56 mm NATO, for instance) in FMJ show that while they definitely produce less of a temporary wound cavity than a hollow point or soft point, they do NOT simply slip through the target making an ice-pick style wound. I found a video showing a soft point generating a five-inch wound cavity while the FMJ created a three-inch wound cavity.
At higher velocities, like the 5 km/s quoted for the "heavy needler", inertial forces during impact are so high that tensile forces can be neglected without seriously affecting the results--that is, both the projectile and the target can be considered liquids for calculating the results.
It's worth noting here that the kinetic penetrators fired by the Abrams tanks typically don't exit the other side of their target, and they're not moving at 5 km/s. More velocity doesn't lead to more penetration at these speeds.
Basically, I'd expect a 3 mm dart at 1000 m/s to make wounds more or less indistinguishable from a modern small caliber rifle cartridge like the 5.56 mm NATO, and a 4 mm dart at 3000 m/s to cause wounds that look like they were made by explosive rounds.
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