March 13, 2005
Some More Ballistics
In the early days of my blog I already wrote about bullets and basic ballistics, and now the time has come for some more discussion of the matter.
When a bullet impacts a target, there are basically three possible outcomes: penetration, deformation/disintegration and ricochet. Penetration means that the bullet enters the target (and remains embedded into it, or exits from the other side); in the second case the bullet will deform upon impact withouth penetrating the target but losing a great amount of its energy - in the extreme case, it will disintegrate in minute fragments; ricochet is when the bullet bounces away retaining a considerable fraction of its energy (and having suffered some damage, usually).
As a rule of thumb, bullets will penetrate soft targets, and smash against or ricochet off hard targets. Which targets are hard and which soft is relative to the properties of the projectile: a 5 mm sheet of ductile steel is a hard target for a lead or soft-nose handgun bullet, but a soft one for an armour-piercing rifle bullet. Other factors also exert influence: angle of impact (at low impact angles, ricochet is more likely even from soft targets); shape, weight and speed of the bullet - fast and slender bullets (and with a high weight/cross-section area ratio) penetrate more than fat and slow ones. But all these subtleties would go out of the scope of this article.
Relative to a military Full Metal Jacket, or even AP bullet, a car's seats padding, human bodies and even the thin sheet metal cars are made of are all quite soft targets. (D0 you understand where I'm going, yet?). So, if your fire a burst at a car with your M240 machinegun, you will find that most of the bullets will just pass through the car - some may remain embedded in the strongest parts, like the engine block. Slugs may be standing on the seats only in rather exceptional circumstance: if the car receives fire from considerable distance, and thus the bullets have just enough kinetic energy left to penetrate the doors (or windows) and then simply fall down. I think it would take a lengthy experimental campaign to find the exact conditions that make this happen.
So, it is extremely improbable (borderline impossible) that Giuliana Sgrena could pick up "handfuls of bullets" from the seat besides her (not to mention that such bullets would be scorching hot). I suggested as a what-if scenario that she meant spent casings - for ignorant people, there is little difference between bullets, casings and completerounds cartridges - but there are no accounts whatsoever of anyone ever opening fire from inside the car, so this is a dead-end. Thus, we are left with only two explanations: either Sgrena deliberately added this false detail to embellish her story (which is changing faster than March weather, by the way), or she was so shocked to mistake glass fragments for bullets.
The soldiers who were manning the checkpoint come from the New York Army National Guard, 69th Infantry Regiment of the 42nd Infantry Division. This article adds to the whole Sgrena Incident story, and gives a good perspective of the kind of problems soldiers have to face at checkpoints. Tips to Charles and Darth Misha for pointing to these articles.
When a bullet impacts a target, there are basically three possible outcomes: penetration, deformation/disintegration and ricochet. Penetration means that the bullet enters the target (and remains embedded into it, or exits from the other side); in the second case the bullet will deform upon impact withouth penetrating the target but losing a great amount of its energy - in the extreme case, it will disintegrate in minute fragments; ricochet is when the bullet bounces away retaining a considerable fraction of its energy (and having suffered some damage, usually).
As a rule of thumb, bullets will penetrate soft targets, and smash against or ricochet off hard targets. Which targets are hard and which soft is relative to the properties of the projectile: a 5 mm sheet of ductile steel is a hard target for a lead or soft-nose handgun bullet, but a soft one for an armour-piercing rifle bullet. Other factors also exert influence: angle of impact (at low impact angles, ricochet is more likely even from soft targets); shape, weight and speed of the bullet - fast and slender bullets (and with a high weight/cross-section area ratio) penetrate more than fat and slow ones. But all these subtleties would go out of the scope of this article.
Relative to a military Full Metal Jacket, or even AP bullet, a car's seats padding, human bodies and even the thin sheet metal cars are made of are all quite soft targets. (D0 you understand where I'm going, yet?). So, if your fire a burst at a car with your M240 machinegun, you will find that most of the bullets will just pass through the car - some may remain embedded in the strongest parts, like the engine block. Slugs may be standing on the seats only in rather exceptional circumstance: if the car receives fire from considerable distance, and thus the bullets have just enough kinetic energy left to penetrate the doors (or windows) and then simply fall down. I think it would take a lengthy experimental campaign to find the exact conditions that make this happen.
So, it is extremely improbable (borderline impossible) that Giuliana Sgrena could pick up "handfuls of bullets" from the seat besides her (not to mention that such bullets would be scorching hot). I suggested as a what-if scenario that she meant spent casings - for ignorant people, there is little difference between bullets, casings and complete
The soldiers who were manning the checkpoint come from the New York Army National Guard, 69th Infantry Regiment of the 42nd Infantry Division. This article adds to the whole Sgrena Incident story, and gives a good perspective of the kind of problems soldiers have to face at checkpoints. Tips to Charles and Darth Misha for pointing to these articles.
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