Supposedly a flying bullet is very hot (supposedly it can be 100–300°C or 212–572°F on arrival)
How does it affect the wound?
Does it burn the skin it first touches before cooling down more? Does it create air bubble inside the body in the first seconds after contact? Etc
A 9mm bullet weighs around 9 grams, and lead has a specific heat capacity of 0.129 Joule per degree celsius per gram, meaning there's (300-39)°C x 9 gram, x 0.129 = 254 Joules worth of heat in your theoretical bullet that would need to be dissipated in the wound.
1 gram of water can absorb 4.18 Joules of heat to increase by 1°C, so if your affected body part has 20 grams (20 milliliters) of water/blood close to the bullet, then that blood would heat up by 254 / (4.18x20) = 3°C.
And that's assuming the bullet only contacts 20mL / 0.68 fl Oz worth of blood... There simply isn't enough heat energy in a bullet to burn anything inside us.
yep, to your last point, since blood is always circulating, it's going to carry any heat from the area immediately around the bullet throughout the body. So the amount it would heat up a full 70+ kg person is completely negligible. Also, that high temperature for the bullet would be mostly the outside. Depending on how far it travels before hitting someone, it may not have time to get heated all the way through.
It's even worse because the heat inside the bullet needs o move to the skin before leaving into the surrounding wet orgnaic matter, preading the (minucule) heating over time. And since a wound tends to bleed, the heat get carried away as fresh blood replaces the old.
The heat of the bullet can have some impact on the wound, especially if it doesn’t go all the way through a person. Nerve and tissue damage for example.
But generally, the bullet is going so fast that there’s not nearly enough time for the temperature of the bullet to make a difference compared to the speed of it.
It doesn't. Essentially it doesn't get hot enough to cook or burn flesh.
That's just Hollywood spin.
Others have covered the speed the bullet moves and some math about heat absorption, but let me just add that any damage caused by the heat of the bullet is always going to be vastly secondary to the actual wound cavity of the bullet wound itself. Compared to "you just got shot" the heat is insignificant.
As others have said, the bullet is moving way to fast to have any impact. A very simple way to see this yourself… put a pan on a burner on the stove and turn it on high. You can get the pan up to a similar level of heat to what you describe above. Assuming there’s no liquid in the pan, you can very quickly touch the pan and move your hand away, and depending on precisely how fast you do this, you will feel nothing to maybe feeling very briefly hot, but again only lasting a fraction of a second with no damage to your skin. Then realize that however fast you are moving when you do that is roughly 10 times slower than a bullet would be traveling.
This is assuming the bullet exits the body as rapidly as it entered. What if it comes to rest inside the body?
Even in that scenario, assuming it’s a bullet from a pistol, it’s going to weigh under 10 grams. Even if it was a bigger bullet from a rifle, you are talking 15 grams tops. Your body is going to rapidly cool the bullet rather than the other way around. It’s like how you can put out a candle flame with your fingers despite the flame being over 1000 degrees.
It doesn't just matter how hot something is, it also matters how well it can transmit that heat to something else and how much capacity it has to hold that heat.
An oven can get really hot, but even at 450F you can stick your hands in to mess around with stuff in there with only mild discomfort. But you wouldn't last one second of sticking your hands into a pot of water half that temperature (boiling) without getting a burn.
Similarly, if you have a thick dutch oven in that oven that's been sitting there for 30m, you're going to scald your hands if you try to pick it up bare-handed. On the other hand, you can have a sheet of aluminum foil sitting in there all day that you can basically pick it up straight up out of the oven with your fingers.
The bullet has direct contact, but is likely going to be moving too fast to have much time to actually transmit its heat and also most of them are pretty small so a hot bullet won't have that much total heat to transmit to do much damage.
If the bullet does stop and doesn’t pass through it does have heat but it usually will mushroom or be pretty small and dump its heat pretty quickly. Shrapnel can be much larger and if stuck inside can cause burning and visible smoke out the wound.
So a self cauterizing bullet?