mythbusters ? if a bullet is launched fast enough can it catch on fire?

Anything will catch on fire if it goes fast enough. The problem is getting it there.

All substances have a flash point, where they burst into flames once at a certain temperature. In order for a bullet to reach it's flash point, it would have to go so incredibly fast that the friction from the air causes it to heat up and catch it on fire. I don't know what the flash point of copper or lead is, but I tend to think it is unreachable for humans.

However, there are incendiary/tracer rounds which have phosphourous or a similar material on them. They catch on fire due to the black powder explosion and reacting with the heat from air friction (I think). You can see them travel along, which is why they were useful for WWII pilots.

Not EVERYTHING will burn. It will melt/vaporize before then.

thanks bfishboy1 is right sovietspyguy is wrong

bfishboy1 has no idea what he is talking about.

The melting point of copper is 1980 degrees F.
Lead will melt at 621 F and boil at 3180 F.

If you fire a bullet fast enough for the lead to melt and boil then you no longer have a bullet.

Tracers have a hollow copper or steel jacket with a phosphorous compund in the base. The hot gases generated by the burning gunpowder propels the tracer out of the barrel and ignites the phosphorous compound. Air friction has ZERO effect on whether or not a tracer ignites. The confusion comes from the orange paint used on the tips of tracers to differentiate the loaded rounds from standard ball ammo.

Not to be picky or anything, but I don't think that metal can catch fire. I know it can be melted, boiled, and even vaporized. I mean to burn does it not have to have a fuel source that will sustain a flame. Here are the melting, boiling, and vaporization points for lead;
Melting point 600.61 K
(327.46 °C, 621.43 °F)
Boiling point 2022 K
(1749 °C, 3180 °F)
Heat of vaporization 179.5  kJ·mol−1
Lead does not have that high of a melting point but still beyond what you are discussing. Just think of how fast a bullet would have to travel to build up to 621.43 F from friction alone. All you did was melt the bullet no fire.

Some metals like magnesium can in fact burn. Whether a metal burns or not depends on how reactive it is with oxygen. Most metals just oxidize slowly even at high temperatures then they melt and boil. I have seen evidence that the exposed lead tip on softpoint rifle bullets may show some signs of melting due to air friction. The skin temperature of the SR-71 could reach 500F at 2000mph which is 3200fps (well within normal rifle velocities). This is close enough to the melting point of lead that it can soften and deform slightly in flight.

I did not know that, thanks bernieb90.

Here is link to a good article with some thermal imaging done of a bullet in flight.

http://www.corebyindigo.com/PDF/articles/AdvImg3-04.pdf

If you substituted a bullet for a meteorite approaching the Earth at high velocity, (some 40,000 mph in many cases) it would "burn up" as it encountered the atmosphere.
That is, it would vaporize and melt, and bits of it would fall away as glowing chunks.

Just as meteorites do.

Whether this amounts to "burning" is a fine point. The metal is being heated to the point of melting and incandescence.

2 things, with magnetic rail guns the slug goes so fast that the metal on metal conact accually makes a plasma arc at the end of the rails, this isnt considered burning though, and meteorites vaporize but they are going fast enough to compress air to the point that it glows, so to make a bullet "burn" it would either have to be flat and going really fast (7mps) or it would have to be made out of an alkali metal