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Bullet Temperature

Discussion in 'General Gun Discussions' started by Blofeld, Sep 21, 2008.

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  1. Blofeld

    Blofeld Member

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    Anyone have any idea on how hot a bullet is when it reaches a target? Is there a formula to figure out what temperature a .22 fired from a rifle at, say, 50 meters would be?

    And to you handloaders/ metallurgist guys, at what temp does lead melt?

    Thanks in advance.:D
     
  2. scrat

    scrat Member

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    ideal termperature for casting is 700 i believe it starts to melt around 600
     
  3. Blofeld

    Blofeld Member

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    Okay, so out of the barrel would be significantly less. Hmmm.
     
  4. scrat

    scrat Member

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    not too sure out of the barrel. The blast and heat produced from the fire may only heat the back end at the time the bullet is exiting the barrel as its happening so fast
     
  5. 230RN
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    Not too helpful, but maybe it's a start...

    I recall, but cannot document, that some hard-driven bullets like the .220 Swift are nothing but little gilding metal bottles full of molten lead as they zoom downrange. When overdriven and over-spun, they may fly apart, leaving a little trail of blue smoke... which is (again, I am told) a spray of this molten lead in midair.

    This "blue trail," without an accompanying hole in the target, has been documented many times in this and other gun sites.

    So, in the spirit of helpfulness, I looked it up in Hatcher's Notebook and found he has a rather muddy description of the distribution of the energy available from a pound of powder. Unfortunately, he does not give a direct figure for the temperature of the bullet, only "heat energy due to friction" of 212.0 Calories out of the total of (I think) 2864.0 Calories available in the .50 BMG from the powder charge.

    It is hard to tell from his accompanying table of heat distribution in that single .50 BMG round whether this "frictional" heat goes entirely to the bullet or part to the bullet and part to the barrel. If anyone smarter than I can make better sense out of that table, please say so. (Cf. p 399, op cit.) I am sure that if we knew for sure what portion of this 212 Calories actually went to the bullet, calculation of its temperature would not be dificult, knowing its mass and composition.

    For those of us who have ever done "The Hot Brass Dance," where an ejected case falls down your shirt, 131 Calories goes into heating the brass case during firing --or about 5% of the total. (Again, for the BMG. I see no reason the proportion itself would not hold up for most CF rifle rounds.)

    (Note: Calories with a capital "C" are "kilocalories," that is, 1000 times the heat energy of the "calories" with a small "c" which we use to measure the energy in foodstuffs. I think nowadays they use "kC" for this same "kilocalories.")
     
  6. BADUNAME37

    BADUNAME37 Member

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    Let's put it this way. I shot a Barnes 275g bullet that went through a plastic trash can full of water. The bullet penetrated 30" of water and I immediately saw it shining in the grass next to the trash can after I shot.

    I went to pick it up and it was so hot, I nearly burned my fingers. In order to hold it, I had to toss it back and forth between hands until it cooled.

    Considering that the water probably helped to cool the bullet somewhat, I would estimate that the bullet was pretty hot.
     
  7. 230RN
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    230RN Marines raising the left-leaning Pisa tower.

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    ^ That's the problem... separating the heat in the bullet while it is going downrange, versus the heat due to impact with and friction while going through the water --or whatever finally stops it.

    What we need is a little itty-bitty teeny tiny telemetering transmitter embedded in the bullet to give a readout of temperature whilst the bullet is in "free flight." :)

    And in a vacuum. Even friction with the air will heat the bullet... which is why it slows down.

    Just taking a SWAG stab at the problem, I would say that when it leaves the barrel, the base of the bullet for "normal" jacketed bullets is around 400-500 dF due to the hot gases pushing it + bore friction + engraving of the rifling. After all, hard-driven cast lead bullets have their bases partially melted due to this factor... which is why I spent so many hours crimping gas checks onto .357 Mag cast bullets.

    Maybe I should drop the "S" from the "SWAG" acronym, leaving just the "Wild-@55ed-Guess" portion.

    And maybe the problem of separating all the variables is why Hatcher's table is so muddy. Even the US Army Ordnance Department couldn't figure it out. ;)
     
  8. Blofeld

    Blofeld Member

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    So then it actually becomes molten lead? I retrieved some bullets, looked at them, and they had a melted candle wax appearance to them. But I couldn't reconcile in my head that they got that hot. Very interesting.
     
  9. 230RN
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    230RN Marines raising the left-leaning Pisa tower.

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    With the .22 LR, they're designed to "upset" to fill the rifling. As manufactured, the back half of the bullet is smaller than the front half, and has to get "bumped up" to the full diameter of the rest of the bullet during firing.

    Sorta like, but not exactly like Minie Balls. I doubt that .22s actually partially melt, but their final appearance after they stop in some media might give them a pretty polished appearance. I don't think they are pushed that hard, but that's another WAG.

    I fired some into a deep fresh snowbank one winter, and the following spring I found them on the ground, and most of them were in literally perfect shape. There was some corrosion starting on some of them, but they looked as if they had been caught by a soft-handed angel and gently deposited on the ground.
     
  10. Blofeld

    Blofeld Member

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    The ones I recovered were .380 Silver something-or-other. I got them as SD rounds, fired them into newspaper to check expansion, and noted the melting effect. I just used .22 as a standard reference point for the question.

    But the answers do raise the point that different bullets are more prone to heat faster, sometimes with catastrophic results.
     
  11. WAID

    WAID Member

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    Although there can be some surface melting of the bullet there is no possible way for the interior to melt without the exterior melting in this situation. The blue puffs from high speed rifles can not be from that, but could easily be the bullet itself just breaking up, at high speeds the RPMs attained are enormous and lead even alloyed is not a strong metal. Add a deep hollowpoint common on bullets like that and they are even weaker. The reports I have heard of where the bullet disintegrated involved them hitting a blade of grass or something like that at high speed. A 220 swift at 4000 fps in a 1 in 12" twist is spinning at around 240000 rpms in a 1 in 14" twist it would be around 205000 rpm.

    Lead alloy data
     
  12. Odd Job

    Odd Job Member

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    Vincent Di Maio reported on some experiments where bacteria were placed on the surface of bullets. The bullets were recovered from the target medium and the bacteria were successfully cultured from those fired projectiles.
    So certainly these projectiles are not hot enough to be sterilised upon firing. I think the temperature of these rounds is often over-estimated.
     
  13. BADUNAME37

    BADUNAME37 Member

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    I concur with the heat not being so hot as to destroy bacteria as I have read that article myself.
     
  14. Czar

    Czar Member

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    Ya'll are forgetting the effects of aero-heating from the bullet passing super-sonic through the air. Air friction is considerable at those speeds (see heat shields on returning spacecraft). supersonic flight + dense air = friction = heat.

    This is not as simple a question as it seems with all the variables… The easy way would be a bullet that reports telemetry and I imagine that it would be hotter at the target than at the muzzle. Other than that, this becomes a helluva Thermodynamics problem and well… let’s just say thermo is not this mechanical engineer’s forte.

    I would be shocked if the combination of all factors would cause the bullet to melt in flight. I would tend to think a more likely mode of failure is too much rotational energy causing centripetal force to tear the bullet apart as seen on several videos of .223 that are hot loaded. One thing to remember about the “candle wax” is that when metal hits a hard surface with a lot of energy, the metal actually flows in a liquid state for a moment. Lead will act a bit different since it is softer, but imagine nickel/copper coins being minted. They mint the image by the use of high pressure stamps on relatively cool blanks and the metal flows into the design.

    Just some thoughts… as I said, this isn’t a straightforward answer.

    Heat sources:
    Heat from the powder burning.
    Friction from the barrel
    Friction from the air
    Energy dissipation from impact with target


    Cooling sources:
    Quenching from the cold(er) air
    Quenching from any liquid target.
     
  15. brickeyee

    brickeyee Member

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    They fly apart from centripetal force.

    They have simply been overspun and exceeded the lead and jacket strength.

    The lead is not molten.

    Go smack a 2 pound drilling hammer in to a lead bullet.
    It will look rather squished, but nothing melted.

    Lead is malleable, and at rather low pressures.
     
  16. 230RN
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    Actually, structural disruption because of the spin was my first thought when I heard of this "blue smoke" thing with the .220 Swift mahy years ago. You will note the qualifications in my orginal statement. I didn't want to bring it up directly because I thought it would muddy the water and I had never heard anyone else expound the spin theory of disintegration. (The first time I calculated the RPM, I thought my calculator was surely broken.)

    Yes, we need a teeny tiny telemetry system. As I said.

    Yes, there are too many variables to be assesed without clever laboratory experimentation. As I said.

    Yes, there would be heating in the air. As I said.

    Yes, surface melting, as on the bases hot-loaded lead non-gas-checked bullets. As I said.
     
  17. Jim K

    Jim K Member

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    When a bullet is stopped abruptly, as when striking a steel plate or a rock, its energy is converted to heat that may (depending on the remaining energy) be enough to melt the bullet or the plate. That is how AP bullets work; the bullet energy becomes heat, which melts or softens the steel, allowing the core to penetrate. If the steel is thick enough that the heat dissipates quickly, the result is a crater with little "splash" marks, or even a core stuck in the steel as it solidified.

    If a .22 bullet is fired at a flat rock (I know, not recommended) you can look at the rock and see the spatter of lead droplets showing that the bullet actually melted.

    That also is what causes bulged barrels; when the bullet stops on an obstruction, the heat released is enough to soften the barrel metal and the pressure bulges the barrel. (Yes, I know some folks just refuse to believe that, but it is what happens.)

    Jim
     
  18. TexasRifleman

    TexasRifleman Moderator Emeritus

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    Some people SERIOUSLY have too much free time :evil:
     
  19. Auburn1992

    Auburn1992 Member

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    Isn't it just the bullet shattering and leaving some pieces behind?

    I shot a pellet gun like that and found some of the lead still stuck. I wouldn't think pellets would be too hot.
     
  20. Howard Roark

    Howard Roark Member

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    A .223 at around 3000fps is about 513deg one yard from the muzzle.
     
  21. 230RN
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    ^ Infrared pyrometer? Why didn't I think of that? (Gives self dope slap.)

    Documentation, please? I would like to see if an IR pyrometer (or any sensor) could react that quickly.
     
  22. Howard Roark

    Howard Roark Member

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    ^ You get the cupi doll. High speed digital thermography.

    Focal plane arrays or FPA are used to sense infared radiation. They are used for missle guidance systems so yes they can react very fast.
     
  23. Blofeld

    Blofeld Member

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    So if lead melts at 600, and a .223 gets up to 513, then the bullet doesn't melt, but it's close, correct?
     
  24. ambidextrous1

    ambidextrous1 Member

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    And at that temperature, it will be softer and more malleable & more ductile.

    I vaguely recall the use of "tempilsticks" which were used to mark the surface of critical metal structures. They were available in several temperature ratings, and would irreversibly change color if their temperature rating was exceeded. That's not telemetry, but it is recoverable evidence of the thermal history of an object...
     
  25. Blofeld

    Blofeld Member

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    Okay, so I saw somewhere that sniper spotters can actually see a trail where the round heats water vapor as it goes downrange. If water boils at 212 degrees, would that not kill bacteria on a bullet?

    And why is everyone here smarter than me?:uhoh:
     
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