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Please excuse the title of the question, there is physics involved here, but I can't think of a way of writing the title without it being more to the point of the question.

A cowboy film is pure drama, and I don't normally expect any correct physics to come from Hollywood. My question is based on watching old "Gunsmoke" episodes during which, each time an actor is shot, even if he is hit in the body far away from a vital organ, the movie doctor says words to the effect "That bullet has got to be removed now".

Far more important though, is that this may also be the case today, I just don't know.

My question is: if the bullet is powered by a very hot stream of gas to fire it, after which it travels through the air at an average speed of 1,700 mph (2,740 kph), where friction from the air slows it down, (but may also heat it up), then the bullet may be essentially sterile in the short time it takes to hit the "cowboy", and unless it's lodged near the heart say, I wonder am I correct in assuming there is no rush to remove it?

In fact, the bullet may be so hot, it may cauterize the affected area.

Over longer distances, say from a rifle shot, this may not occcur and the bullet may well be air cooled enough be a source of infection. This is simply a guess on my part though.

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closed as off-topic by DanielSank, user36790, John Rennie, Sebastian Riese, Kyle Kanos Oct 6 '15 at 11:43

  • This question does not appear to be about physics within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ So, what's the question? If you're asking generally about whether or not bullets should be removed, then this is a medicine question and not really on-topic for this site. There are many factors affecting how a foreign object affects the body. If you want to reword the question to ask specifically about how hot a bullet gets in transit then we can make a nice physics question. $\endgroup$ – DanielSank Oct 5 '15 at 18:39
  • $\begingroup$ From a sterility perspective, perhaps, but from a "damage my internal organs" perspective, definitely a rush to remove it. Either way, this is probably better suited for the medical community. $\endgroup$ – Kyle Kanos Oct 5 '15 at 18:41
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    $\begingroup$ I'm voting to close this question as off-topic because it's a question about medical trauma. A revised version asking specifically (and only) about the temperature of a flying bullet would be totally fine IMO. $\endgroup$ – DanielSank Oct 5 '15 at 22:36
  • $\begingroup$ I can't comment on the medical aspect, but on the heat of a bullet aspect, this video is loosely related. You can see a fired bullet spinning on the ice and it's not melting the ice much, which you would expect it too if it was hot enough to cauterize a wound. youtube.com/watch?v=foZlciP6gUQ so the physics part of your question, while I would think a bullet hitting the body might be quite hot, but, maybe not. There's also, no shortage of articles and conversations on "do bullets need to be removed" if interested / not physics though. $\endgroup$ – userLTK Oct 5 '15 at 23:24
  • $\begingroup$ There's also a rather interesting description of the attempt to remove the bullet from President Garfield in here, a few comments in. ask.metafilter.com/73088/… (A fun read, even if it's not physics). $\endgroup$ – userLTK Oct 5 '15 at 23:30
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Assuming that the bullet flies at Mach 2.0, the temperature at the front of the bullet is about the same as the surrounding air (since at that relatively low Mach number, there is little thinning of the boundary/shock layer to cause aerodynamic heating). I do not know how much heating there is from the gases in the chamber/barrel (it may be significant, but as you suggested, with a long distance shot, the temperature will settle back to ambient).

One reason suggested for removing bullets like that is that there may be cloth inside the wound, "brought along" by the bullet on entry, which is a great place for pathogens to breed/enter the body.

$$\frac{T_{\text{bullet}}}{T_\infty} = \frac{T_{M=2.0 (\text{pre-shock})}}{T_{M = 0}}\cdot \frac{T_{\text{post-shock}}}{T_{\text{pre-shock}}}\cdot \frac{T_{\text{bullet}}}{T_{\text{post-shock}}}$$

$$\frac{T_{\text{bullet}}}{T_\infty} = \left(\frac{5}{9}\right)\cdot 1.6875\cdot \frac{1}{0.9375} = 1$$

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  • $\begingroup$ Thanks very much for taking the time to answer, it was one of those niggling questions that had me throwing things at the TV, convinced as I was that the bullet would be sterile:) $\endgroup$ – user81619 Oct 7 '15 at 12:42
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A basic question is - how hot does a bullet actually get? Here is an answer. Note that the biggest effect is frictional heating in the barrel lands, which produces peak temperatures of ~320 C. Also note, though, that the affected areas are quite small in proportion to the overall bullet size, so the average bullet temperature rise is also quite small. Although the propellant gases are quite hot, they only contact the base of the bullet for a few milliseconds, which is not time for the heat to penetrate very far into the projectile.

As has been remarked, the big problem with bullet wounds which are not immediately fatal is the introduction of dirt and cloth, and getting debris out of the wound is important to avoid infection. But it's not urgent if you can't go in and actually repair organ damage.

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